Under
Mesklinite 4
(2000)
Hal Clement

What Has Gone Before

	Mesklin is the single "planet" of 61 Cygni A, the brighter member of a binary system approximately eleven light years from Sol and Earth. While several times as massive as Jupiter, it is not a gas giant; like Earth, it lost nearly all its hydrogen during formation. Predictably, most of its mass is concentrated in a core of degenerate matter, and its total volume close to that of Uranus or Neptune.

	It has attracted astrophysical attention since its first well-resolved images were obtained, for several reasons.

	First, shape. It is close to rotational instability; with a day of less than eighteen minutes, its equatorial radius is more than twice the polar one. Inertia gives it an equatorial surface "gravity" only three times that of Earth; the polar regions, lacking centrifugal effects and far closer to the ultradense core, would flatten a human being under several hundred times his normal weight.

	Second, physical nature. The original accretion heat has been lost completely enough to leave the surface temperature at roughly radiational equilibrium; the oceans are principally liquid methane, the atmosphere nearly all hydrogen with a surface pressure of about eight bars. It is not clear why settling of mantle mass has not increased its spin rate for the last few billion years so as to cause general breakup and forestall the development and normal evolution of life. (The planet has several rings, which might possibly have formed from such an event; but rings don't ordinarily last for eons.)

	Nevertheless, physicists rather than planetologists had most to say about its original detailed investigation. A remotely controlled spacecraft was landed at the south rotation pole to conduct experiments in the hitherto unattainably intense gravity field there. Much information was transmitted to the researchers at a base on the inner moon, Toory, and much more was expected to be obtained on physical records when the craft returned. Unfortunately, it failed to respond to the liftoff command, causing extreme consternation to researchers of some ten worlds whose people had contributed to the project.

	However, a sop had fortunately been tossed to the planetary specialists and biologists in the form of a manned observing station near Mesklin's equator, where human and similar beings could, with precautions, stand the gravity for a time. Citylike patterns had been observed, with some uncertainty, in the mid-latitudes; and while there was little reason to hope that beings evolved for such conditions would be found anywhere near the equator, efforts involving firework displays and extremely loud sound broadcasts had been made to attract their attention.

	These had been surprisingly successful. Barlennan, a sailor-trader-explorer of Mesklin's seas, had discovered the station. Charles Lackland, sole staff member of the outpost, had managed to make linguistic contact and, after much effort, teach some of his own language to Barlennan and learn some of the latter's Stennish.

	At the start of Mission Of Gravity, a bargain had been worked out. Barlennan's crew would travel to the south polar regions, and try to salvage as much as possible of the information in the grounded rocket. They were physically able to stand even the extreme gravity of the planet's poles; their fifteen-inch-long hemicylindrical bodies, supported on numerous stubby caterpillarlike legs, were tough. They were neither arthropods nor vertebrates; their flesh was resilient enough to need neither internal nor external skeletons. They did not breathe in any usual sense; their energy was derived from reducing highly unsaturated hydrocarbons and similar compounds with atmospheric hydrogen, and they were physically small enough for adequate supplies of this gas to reach their extremely small body cells by diffusion. Their ability to use oral speech stemmed not from modified breathing apparatus but from evolved organs originally corresponding to propulsion jets like those of terrestrial cephalopods.

	The season was propitious; the deal was made near the end of the brief winter, and Mesklin's southern hemisphere midsummer nearly coincided with the periapsis of its orbit, so much of the journey would enjoy daylight (Mesklin's year is some eighteen hundred Earth days in length, and its orbit quite eccentric).

	The Bree, Barlennan's ship, was a mosaic of individual rafts equipped with sails and centerboards, and represented a fair example of his species' technological status. The ability of Lackland and his fellows to travel through the air aroused several different emotions in the captain, largely acquisitive and envious ones. He was perfectly honest by his own standards, but hoped to pry large amounts of usable, and saleable, know-how from his customers while carrying out their wishes—knowledge which he at first took for granted the Flyers would never supply willingly, and certainly not freely.

	The trip to the pole involved first a long overland journey to an ocean strange to the Bree's crew. This was managed by towing the vessel behind a tanklike vehicle driven by Lackland. During this stage of the mission, the Bree personnel encountered a number of adventures which put serious strains on their normal conditioning to avoid either falling, becoming vulnerable to falls by climbing, or allowing anything to fall on them. Events even opened their minds to such concepts as throwing.

	Having to climb to the top of the tank to escape rocks being rolled downhill on them, with essentially no time to debate the choice, was a typical experience. A more extreme one was provided when the tank's progress was blocked at the top of a cliff extending indefinitely in both directions across its path, forcing Bree and crew to descend somehow. The sight and sound of a nearby waterfall did not help Mesklinite feelings.

	By the time the ship and crew had been lowered by block and tackle, raft by raft, to the ground below, reassembled, and refloated on the river fed by the waterfall, none of the crew members was as he had been. Whether any of them, Barlennan and his first mate Dondragmer included, was still sane by Mesklinite standards was debatable.

	But at least the river led to the right ocean—the Flyers could assure them of that—and all were willing to go on. Lackland had to turn back, since there was no way to get the tank down the escarpment, but he had provided the natives with a number of communication sets complete with cameras. These could be used to talk with the Flyers on Toorey, and allow the latter to give advice and to see what Barlennan and the others were encountering.

	But even at sea, familiar as it should be, there were disturbing experiences. The sailors were used to storms, of course, and even knew why ships should stay well away from any land during them: ocean level, even in high-gravity latitudes, rose enormously in the extremely low-pressure centers of such disturbances, due to the tremendous Coriolis force. A ship could find itself stranded surprisingly far from liquid when things had quieted down. Avoiding land on an unknown ocean, however, was difficult even with help from above, and at one point while at the still-low seven-g latitude, the Bree found itself floating on a pond in a valley drained by what had once more become a narrow streamlet almost surrounded by low hills—low by Flyer standards—on a presumably not-too-large island.

	The local inhabitants proved to be of their own species, but they flew. They used gliders, launched by elastic cables, kept aloft by their pilots' knowledge of wind patterns. Here Barlennan began to realize that the Flyers were at least sometimes willing to supply him with knowledge if he needed it. They explained how the gliders worked, though using seagulls as an analogy proved ineffective, and helped with still more information when disagreement with the locals made an escape necessary. Dondragmer was able to grasp the concept of, and to build, a differential hoist to remove a group of deep-driven stakes barring the Bree's course downstream to the sea.

	At still higher latitudes, the thin-walled dugout canoe which Barlennan had acquired along the way and was using to tow supplies collapsed and sank from second-order gravity effects, and once more the Flyers proved willing to explain, this time with no real emergency apparently involved. The Mesklinites already had a general grasp of Archimedes' principle, of course, but would probably not by themselves have figured out the effect of rising hydrostatic pressure near its keel on the displacement of the "hollow boat."

	The travellers eventually reached the south polar continent, worked their way up a broad estuary and its source river to a point only a few miles from the grounded rocket, to find their way blocked by another cliff—almost perfectly vertical and some three hundred feet high. 

	They were at the bottom this time.

	Observation from space indicated that the escarpment completely circled a continent-sized area, and sent the planetary physicists arguing fiercely how any such phenomenon could have occurred under hundreds of gravities. This did not help the mission.

	Observation from above showed one break in the cliff some hundreds of miles farther up the river. The ship was tacked up to this site, finding a region where the escarpment had collapsed (why only here, people wanted to know). Barlennan and part of his crew worked their way up slope and across the boulder-strewn continent above, while the Bree and the others went back downriver to wait at the point nearest the rocket. The crew above finally reached the cliff top above this spot, and set up block-and-tackle connection with the ones below as had been done with the first cliff long before. 

	They then moved themselves and supplies to the site of the rocket itself—which towered far above them. Because of the gravity, it would have to be disassembled and each part removed and studied from the top. The Mesklinites solved this final problem by spending many, many days burying the probe. Eventually they could reach its nose cap and start removing module after module, with no serious risk to the pieces by dropping them, under instructions from above.

	At this point Barlennan renegotiated the contract, insisting on unrestricted access to any scientific information the aliens could supply. The aliens, after convincing him that at least some of this knowledge would be beyond his grasp without a long period of basic instruction, agreed to start the latter—and they agreed much more easily than Barlennan had really expected in spite of the events along the journey. He was a little disappointed that it had been so easy; but Dondragmer, a basically curious being, was not bothered in the least.

	Salvage and schooling began together, and went on for many thousands of Mesklin days. Mission Of Gravity ended with the launch of the second Bree—a hot air balloon.

	Under starts some thousands of days later still, toward the end of Mesklin's southern-hemisphere summer, with the dismantling of the spacecraft almost completed, and the planetary physicists pushing hard for a return trip to the equator by ocean. They badly want the Bree to carry an inertial tracker salvaged from the rocket. The thought of the information about Mesklin's interior which should be obtainable on such a trip, with observations from space permitting the separation of inertial and gravitational data supplied by the tracker, is affecting the dreams of human and nonhuman researchers alike.

* * *

	That looks all right. Come aboard, Cookie. Then reach out and light it. Hars, lift—now!"

	Neither crewman acknowledged the orders verbally; they acted. Karondrasee whipped aboard in normal centipede fashion, scooped a coal from the lifting fire into the long spoon waiting for the purpose beside the furnace, reached through the handiest crenelation in the Bree's mostly solid gunwale, and steadied the burning fragment over the frayed-out end of rope fuse beside the basket. He was't bothered by the form of address; there was need for haste, "Cookie" was shorter than "Flight Engineer," the duties overlapped heavily, and he was filling both of them. He was, however, annoyed and uneasy for other reasons; he had had to spend many days treating the three lengths of cord with meat juice and, as he saw it, wasting two of them. As cook of the old Bree's crew he was used to seeing the results of his labors vanish, but he disliked seeing them burn up. That was the annoying part.

	He was uneasy as well, because things might not work this time as they had on the two test burns. The first had not been dangerous, of course; it had simply served to show whether his juice treatment would really turn rope into a useful fuse. That sample was short enough to need only a day or so to make. 

	The second test should either not have worked at all or produced a simple, harmless fire fountain. By doing the latter it had encouraged everyone. Now the third and potentially most dangerous trial was under way.

	The captain seemed unsure, too. He was watching the fuse as closely as Karondrasee was. So was Sherrer.

	Hars was not. He was tending his lifting fire and eyeing the tensely swollen bag of the third Bree. He knew enough about the present test to want the ship to lift quickly, but if it rose too quickly, that would of course be the captain's fault. Hars was obeying orders.

	That last thought was also in Barlennan's mind, and he was watching the delivery of the bit of fire tensely. If he had given Hars his order too soon—

	Strictly speaking, he had. He felt the basket's deck stir under him, and saw the figures on the Flyers' instrument change. He would have stopped breathing for a moment if he had been a breather. Karondrasee, however, also knew the plan, knew what would have to be done if the fuse failed to light, and certainly didn't want to get out and push the coal to the right place while the balloon rose without him. As he saw his spoon rising slowly from its target, he tipped it over without waiting for an order.

	No one actually saw the coal drop; falling, here, was much too fast for even Mesklinite vision. Cook and captain did see, as the air below it was compressed enough to speed its combustion rate by perhaps an order of magnitude, a sudden flash on the ground half an inch to one side of the fuse end. Before either could comment or even curse, the rope ignited—apparently from radiation, but conceivably from a flying spark, though neither witness could vouch for the latter. They didn't really care; the wadded rope-end was starting to glow, and that was all that mattered.

	"Lighted all right?" 

	"Yes." Barlennan didn't bother to look at the block of polymer from which the question had emerged. "Hars, up as fast as you can. Never mind checking wind. I'd like to keep on this side of the rock to see what happens, but getting to the other may be safer and staying out of reach will be safest of all. I wish someone knew what ‘out of reach' was, but if we do blow that way, up will mean a lot more than sideways."

	"Right, Captain. Up it is."

	Up it was. Not rapidly; it took a lot of lift to start an upward motion near Mesklin's south pole, even though once started acceleration tended to be high. That was why more than a thousand feet of fuse had been laid out, and the original test of its burn rate had been made.

	"Please keep this eye aimed at the rock, wherever we go."

	The block spoke again.

	"Right. Sherrer will see to it," the captain responded, still without looking at the communicator. "We have you blocked up far enough to look over the rail already, and he'll wedge the back up more if it's needed."

	"Are you set to turn it too, or will it be easier to rotate the whole balloon?"

	"Much easier, though it'll cost a little lift. It will also make it unnecessary for you to look across the fire. Don't worry yet, it should take half a day to burn down."

	"I never worry. I just wonder." Jeanette Parkos, who had taken up Charles Lackland's communication duties when health had forced him to return to Earth, was rich in comments like that. She had greatly improved Barlennan's Spacelang in the last few thousand days, and to his surprise and in spite of her alien hearing and vocal limitations she already spoke Stennish much more fluently and clearly than her predecessor ever had.

	"I'd appreciate a bit of down tilt whenever Sherrer can provide it," she now suggested. "I can't see up to the horizon, but I can't see down enough for anything within a couple of miles, either. You're a lot closer to the rock than that, according to the tracker readout, and I hope you're closer still when it goes. I sometimes wish this thing had a wider field of view. Of course, I sometimes wish it could zoom closer, too."

	Barlennan was not entirely sure that he shared the hope, though he wanted a good view himself. The Flyer was on Toorey, Mesklin's inner moon. Her communicator would let her see what went on. The closer to the rock the better for her, but nothing could, presumably, happen to her at that distance. Barlennan lacked both the distance and the seeing equipment, and wasn't sure which he missed more. The Flyers had assured him that there couldn't possibly be enough energy in the propellant cell now being tested to lift the rock above it any significant distance, but the Flyers had been wrong before. He remembered vividly the Foucault pendulum fiasco; they had been certain it would give a convincing demonstration, this close to the pole, that Mesklin rather than the sky was doing the spinning. Unfortunately no one, native or alien, had been able to observe the six-inch pendulum's plane of motion; its period was too short, and like any tuning fork its vibration had been damped out by the air a few seconds after it had been started.

	They had all heard it, of course.

	None of the Flyers seemed to remember that now. Barlennan had not seen an explosive in action since Lackland had used his tank's gun so many thousands of days before, since the previous cell test had produced only the hoped-for fire fountain; but he had been told in detail how such substances were used elsewhere in the universe. These accounts, and a vivid memory of the effect of the shells Lackland had used, left him wondering why no one seemed to worry about the behavior of pieces of the rock. Unlike Jeannette, Barlennan was a rather efficient worrier; he had not raised the question with her because he knew the aliens were extremely knowledgeable in spite of their occasional slips, and he still didn't like to look ignorant. Answers beginning with "Of course" bothered him, especially in front of his crew, most of whom were now fairly fluent in the alien common language.

	"Can you tell if it's still burning, and how far it has to go?" the Flyer queried.

	" 'Fraid not. The fire doesn't give any light to speak of by daylight. Too bad there's no night now—though if there were, we'd have to plan pretty tightly so the fire would reach the cell by daylight and we could see what happens to the rock."

	"It might have helped, but since we couldn't be sure just when the fuse would run out—well, it's academic anyway. Even if you could control your landing point well enough you'd probably not have time to get there now, get out, cut the fuse, and start over. We'll just wait and hope. Good work, Sher; I think I see the rock now, though I can't be sure it's the right one. It looks like the pictures we got before, but there are such a lot of them—rocks, I mean—this close to the edge of the plateau that I could be wrong. Too bad that fuse doesn't smoke."

	Since cooking fires on Mesklin don't normally smoke either and other kinds of fire are extremely rare, some minutes were used in explaining the last word; but someone remembered the Stennish for "fog" eventually, and there remained an unknowable length of suspense time when interpretation was managed. The earlier tests had given the Flyers some idea of the fuse burning rate, but the two had disagreed by over ten percent. Tension mounted, therefore, as the minutes passed. 

	Especially for the captain, as Bree Three was drifting toward the rock, keeping Sherrer busy and Barlennan worried. Their height should be great enough now to be pretty safe provided the aliens hadn't overlooked anything important, but there was no way to be sure they hadn't.

	And, in fact, they had.

	There was no flash; the cell salvaged from the rocket's liftoff equipment had been worked as far under the giant boulder as the latter's shape, the hardness of the packed ground, and Mesklinite psychology had allowed. A solid object several body lengths high and wide was not something a sane native wanted close to him, much less extending overhead, though the crew had gotten more or less used in the last hundred thousand days or so to the three-hundred-foot cliff edging the plateau. They were no longer, perhaps, wholly sane by their species' standards. 

	This cell held a directional charge like the other, its individual macromolecules oriented to send all the exhaust in one direction, and had been aimed slightly downward and away from the rock this time. It therefore started by digging up an enormous cloud of dust. None of the aliens on Toorey was an explosives expert, and none had considered all the likely results of blocking what should have been a free stream of hot gas with several tons of dirt, dirt very solidly packed by Mesklin's polar gravity.

	Essentially, all the unit's directional qualities were lost as its reaction products hit ground and were scattered randomly. It might as well have been a half-ton-mass chemical bomb. The big rock did shatter. Being correct on this point did not please the captain as much as it might have; he watched tensely, knowing that if anything did go wrong there would be no time to give Hars a meaningful order.

	None of the large fragments got far, and none could be seen in flight except near the tops of their trajectories, where they produced a hazy, discontinuous roof a foot or more thick and very little farther from the ground for a brief moment. Some of the much smaller stuff reached terminal velocity at other points, both upward and downward, and was visible very briefly to both Flyers and Mesklinites before hitting the surface again. Everything except for really fine dust had settled out before the sound wave reached the balloon. 

	This was least surprising to the natives. The quick-firing gun which had been used during the near-equatorial part of their earlier Odyssey had accustomed them to the sound of explosions, but had given them no clue to the speed of pressure waves in air. Their own voices had a volume astonishing to the Flyers, and they were aware in principle that there was a delay between hooting and hearing, but they had never considered the fact quantitatively.

	The real trouble was that the crew of the balloon had, at the recent briefing, been assured that nothing of this sort should happen with a directional charge; it was supposed to take several seconds to burn out, waste much less of its energy in sound, and eject its gases in essentially all one direction as the earlier one had done. That one had been aimed straight up; this had been supposed to dig.

	Barlennan added another item to his mental file of Flyer fallibilities. It wasn't really needed; the creatures had, carefully and often, made it clear that tested scientific beliefs were always tentative though usually more reliable than speculation. One could never, obviously, be sure that all the relevant data had been secured or properly considered.

	"Hey! Look at that ripple!"

	The alien voice was not that of Jeanette, but the captain understood it well enough. Ripples he knew about. Near the equator they could be watched quite easily, though close to the poles they moved much too quickly to be visible.

	He also did not expect them on solid ground, here or anywhere. The word "solid" was a concept which to him did not include waves, large or small. The phenomenon was very brief; it was lucky he had been looking in the right direction. It was a ripple, flickering across the ground from where much of the smashed rock still lay, in all directions. The quivering of each boulder it passed was quite visible, rapid as the passage was. He realized that the wave had started and gone under the balloon before he heard anything, but only later realized—when it was pointed out to him—that the disturbance must have travelled faster than sound. He didn't bother to ask why even then.

	The alien watchers on the satellite realized that the ripple must be a seismic wave, but none had a really good look at it just at first; it was out of the viewer field, close to the horizon as much of that was, in much less than a second. High-speed cameras had recorded it all, of course, but time was needed to play these records back, and there had not yet been time. 

	One of the Mesklinites, favored by a far wider field of vision, called attention to the real results of the blast.

	"Look!!" The word was a bellow in Stennish, which Jeanette didn't bother to translate to her fellows.

	"Show us! Let us look too!" she cried. "Where? What? Turn the lens!"

	Sherrer was a little slow in responding, his attention being focused toward a spot at the edge of the cliff, half a mile from the balloon and from where the rock had been, and at right angles to the line of sight between these. Barlennan reached for the rotation valve lines, but the balloon was slow in responding as usual.

	Starting at the point nearest the blast, the edge of the precipice was starting to crumble away and, of course, to disappear. Cracks nearly parallel to the cliff face and up to a meter from it were appearing. Others nearly perpendicular to them were also showing briefly; then the outer sides of the prisms they outlined were leaning slightly farther out and promptly vanishing. New cracks closer to the balloon than the new edge appeared immediately, outlining sections which were vanishing in turn. The disturbance was spreading in both directions from the point where it had started—the point where, Barlennan realized, the "ripple" must first have reached the cliff face.

	His memory flashed to the rockfall, hundreds of miles away, where he and some of his crew had first climbed to the plateau tens of thousands of days before. That had not stretched very far along the cliff. Right now his people and vessel, the original Bree, were ten miles along the edge from this new point of collapse and should be safe—

	If this one spread no farther than the other. Neither he nor any of the Flyers had been able to explain what had caused that other fall. A vertical cliff three hundred feet high and of any length at all near a Mesklin pole was unbelievable enough; the now well-determined fact that it completely rimmed a continent-sized area of the giant planet was worse.

	The general layered appearance, which the Flyers claimed to mean sedimentary rock, was hard even for them to reconcile with an unbroken vertical cliff. There should be rock fragments—more reasonably rock powder—at the bottom. All along the bottom. Barlennan had often heard them arguing about whether the perfectly vertical joints in the cliff face implied that the plateau had been lifted or the surroundings lowered, but it had been another of the inconclusive debates which seldom held his attention for long. 

	No guess at what might have caused that local fall had ever come close to explaining why it had stayed local; it was easy to imagine something like a careless footfall's (whose?) starting the break—but what could possibly have kept it from dominoeing both ways the whole ten- or twelve-thousand-mile circumference of the continent? And for that matter, what had studded so many thousands of square miles of the plateau's outer edge with boulders up to truck size, most of them lying on the surface rather than even partially buried? No one on Toorey was in the least surprised that Mesklin showed tectonic activity, and no one was too surprised that this differed in detail from anything familiar to Human, Drommian, and the other researchers' experience. 

	The edges of the plateau which had been seen, only a small fraction of its total circumference, did appear to be sedimentary rock, but this did nothing to make theorizing simpler.

	Would the same unknown cause, or any other, operate to stop the spread of this fall? Were his crew members safe? The original Bree was ashore on the far side of the river, a little farther from the base of the cliff than the scarp itself was high. Many of those below would be away from the ship, farther still from the cliff, hunting, and presumably safe. Others, though, might well be fishing, since the river was a major source of food.

	There was nothing Barlennan could do. The Flyers were still calling for attention. There was nothing they could possibly do either, but they deserved to watch. Barlennan was a responsible and reasonably fair-minded adult, and never thought of blaming them for what was happening.

	The slow swiveling of the balloon finally brought the lens to face the cliff edge, not at the nearest point but well to the right, where the unaffected edge itself could still be seen. The captain stopped the rotation there. The new edge was now much closer to the balloon and—

	And its growth was slowing? Surely it was slowing?

	Barlennan's people, after many thousands of days piling dirt and rocks around the alien rocket in the course of business, had a very clear concept of angle of repose. The collapse couldn't possibly extend much farther back from the original edge than it was now getting, the captain told himself. The whole plateau would never crumble to fragments, obviously. At least, it hadn't the other time.

	But that was not the immediate problem. How far along would the disintegration extend? How safe were his other men? And how would he get his people and the stuff the Flyers wanted to recover physically, such as the inertial tracker, back to the equator if his original ship were lost? Taking the balloon across thousands of miles of ocean was ridiculous; it could carry fuel to heat its air for only a few days, in spite of Karondrasee's endless research into different juices with maybe more effective enzymes. It could not carry the whole crew, even if the stuff wanted by the Flyers were all left behind.

	"We've warned Dondragmer." Jeanette's voice caught the captain's attention at this point in his thoughts. "No one is on the cliff side of the river. A dozen are away hunting. The ones still at the ship are getting as far from the river and the cliff as quickly as they can carry the radio."

	"Can they carry it while keeping it pointed so you can see what happens to the cliff, and tell me?" asked Barlennan.

	"Don said he'd try." That was enough for anyone who knew the mate.

	"Can you see from it right now?"

	"Yes. It's pointed along the cliff in the direction the fall will come from, but the view isn't too steady." 

	"North" and "South" were not useful words this close to the pole, though the latter had been located very exactly long before. 

	"I'd suggest there can't be any danger farther than, say, three times the river's width away from the cliff foot. When they get that far, maybe they could put the set down occasionally to give us a steadier look and better pictures."

	"Maybe. But leave that decision to Dondragmer."

	"Of course. But you still have two cameras besides that one; maybe he could leave it—"

	"We've been using all three. Dondragmer decides. I know what I'd do with my present knowledge, but he's there."

	"All right." There were beings, most of them non-human, on Toorey who might have argued further, but Jeanette Parkos was not one of them. She was very conscious of who was in charge on the surface, and as chief communicator realized clearly who would be blamed if any major disagreement should develop with the Mesklinites. "We'll report to you as well as we can when the collapse gets in sight from where Dondragmer is, if it does."

	"Good. I'm still hoping it won't. That other one we climbed to get up here—"

	"The other one is much narrower than this one is already. Whatever caused it can't have been as energetic."

	Another alien voice cut in. "That's silly! Practically all the energy involved now is coming from falling rock. You have a chain reaction."

	"But that must have been true for the other fall, too!"

	Barlennan turned his attention back to the still-spreading collapse. He had learned long ago the futility of listening to Flyers arguing theoretical points when anything was actually going on. They got too far behind real time much too quickly. No doubt it was because they were too far away to feel personally involved. The captain was not; he turned his eyes back to the explosion site.

	At least, nothing more was flying through the air. Their own climb had ceased, according to the tracker and his own eyes; the balloon had reached its ceiling, which was low because of the rapid decrease of air density with altitude. Hars' efforts were now focussed on keeping its height constant; altitude control was highly unstable. Even a slight dip caused a decrease in balloon volume, and hence a decrease in lift, which tended to make the dip deeper. It was like the hollow boat's behavior so many gravities to the north. Hars had developed a high skill at handling this problem; it had been he who had conceived the deflectors which gave quick control over how much hot air was actually entering the bag, and eliminated much of the control lag involved in merely feeding fuel or sprinkling meat juice on the fire.

	"It's coming." The human voice sounded less excited than the captain felt was appropriate, but Jeanette was not, of course in danger herself. One should make allowances.

	"How close?"

	"It's just come around the point about three miles upstream."

	"How far is the debris spreading out into the river?"

	"I can't tell very well yet. The set is on the ground, or as near as no matter. The edge view I get for the bend seems to show repose at about forty degrees for the stuff near the top, and maybe twenty near the bottom. That would mean anything that's more than about one cliff height away from the original bottom should be safe."

	"That does not quite include the ship," Barlennan pointed out.

	Dondragmer cut in. "There wouldn't be time to get back to the ship, much less to tow it overland any distance, before the fall gets here."

	"All right. Make sure the crew is safe. Head for the site where this balloon was built; that has to be safe, and a lot of our stuff is there anyway."

	"Yes, Captain. We'll start searching for shipbuilding materials at once, when we get there. Have you further orders?"

	"None for now, except when you think you're far enough out to be safe you should set the Flyers' eye where they can see what happens. Remember they can see things over again, and could be able to tell us how best to find and recover anything that gets buried."

	Dondragmer was probably the least susceptible of the Bree's crew to being startled, and had spent many thousands of days burying and then digging out the alien rocket, but the thought of excavating a rockfall jolted him. Several of the crew could tell this. None, however, said anything, and the communicator was set down and pointed as the captain had ordered. The natives stayed where they were afterward, and nervously watched the collapse region as it neared them.

	They could see that the falling material was pretty certain not to reach them, but Mesklinites in general are not calm about anything's falling. Not even Mesklinites with the background of Barlennan's crew.

	The roar of the rocks was loud enough now to drown out even their voices, and there was no conversation as the wave thundered past in front of them.

	From Toorey, the view through the lens involved less emotion, though several of the watchers were already, and everyone hoped prematurely, wondering what the loss of the original Bree would do to their plans. More were observing, in as much detail as the optics allowed, the way new vertical joints appeared closer and closer to the watchers, delimiting sections of rock which began to tilt slowly outward—a slow fall was a phenomenon on Mesklin—and then develop horizontal cracks which shot back toward the areas already bared by the downward disappearance of previously loosened material. The rock above each crack tilted slightly outward and vanished in its turn, reappearing as it shattered on the growing slope below. Lower segments of the falling prisms were just as invisible during their falls, but didn't fragment as completely before coming to rest. The repose angle grew steeper as the eye travelled upward and encountered less and less fine material and more and more large slabs and columns.

	On any other world the details would have been mostly hidden by dust—with or without an atmosphere to suspend it.

	Not on this one.

	The collapse wave thundered past. Dondragmer retained enough presence of mind to turn the vision set to the left, so the Flyers could keep watching its progress. This was just as well, because it let them see its sudden halt.

	The wave was fully two miles past by this time; whatever stopped its progress could not have helped the ship still on the riverbank. But it did stop.

	Within seconds, the debris seemed to have reached equilibrium. The observers, local and offworld, found themselves looking at a new straight-up cliff far to their left extending inward from the former face, roughly toward the grounded rocket. Its lower section was partly hidden by the scree slope so suddenly formed, but what could be seen was as nearly vertical as the original had been.

	Several of the Mesklinites, rendered more nearly insane than their fellows by the events of the last thousands of days, promptly started back toward the cliff, slanting downstream to get a look at the end of the fall. Dondragmer was equally curious but ordered them back. Jeanette interrupted his commands.

	"It's probably safe enough, Don. The stuff must have reached repose angle right away."

	"No doubt you are right, Flyer Jeanette, but we will first bring the captain up to date with events. He could not have seen this, unless the balloon has moved remarkably fast in the right direction. You would know better, but I can't see it from here. Also, you do not mention that the repose angle, if it really is that, is much steeper for the higher, larger fragments than for the much finer material near the bottom."

	"You know," cut in another alien voice, "this will be the first chance we've ever had to get a close look at the rock making up that cliff. We could see it was sedimentary, if horizontal layering means anything, but all we could tell was that the bottom fifty feet or so was light grey in color, the next layer up was a lot darker, and for the rest of the way up there were variously light and dark bands up to the nearly black one at the top. That one's silicate—mostly amphibole, the gear on the rocket told us years ago right after the landing, but this will be the first time we'll be able to tell anything about the other layers."

	"What will we be able to tell?" snapped another. "Just what will color tell us, and what else will we be able to see?"

	Dondragmer, like the captain, tuned out the argument. He had more important problems to face.

	There was no more visible rock motion anywhere along the fall; the stuff must, indeed, have reached some sort of equilibrium. There was no more sound even from the left, where falling material must presumably have taken a little longer to fill space around the new corner.

	But something—the "smoke" described a little while before? well, maybe ordinary fog—was rising from the far side of the river, over the newly fallen material. Even after watching balloons, the sight of something flowing upward was startling. Explanation would have to wait, though.

	There were fragments of all shades and several colors at the bottom of the fall, but the mate was more concerned with what might be under it. What had happened to the Bree? And for that matter, what might have happened to the river? He didn't worry about the captain, who had presumably been almost as much out of danger as the Flyers. After a few moments' thought, he headed toward where the ship had been, ordering a few of the crew to come with him carrrying the communicator, and sending off others to examine the edge of the fall both up and down stream.

	Almost immediately he had a question to ask the aliens above.

	"It's getting a lot warmer as we get near the fallen stuff. Can you suggest why?"

	Even Jeanette could, but one of the scientists undertook the explanation. Not even Dondragmer had really grasped much thermodynamics yet, but many of the natives had a fairly clear idea of energy. Every falling pebble had lost a lot of potential—

	Quite a lot. More than enough, for the stuff originally near the top, to bring its temperature above the melting point of water, one of the aliens figured. Not that any of the natives knew what water was, or that there was any reason to believe there was any around.

	"Better stay away for a little while," the alien concluded his or her remarks. "It shouldn't take long to cool again; your air is a very good conductor of heat. Actually, it must be radiation you're feeling; there ought to be a pretty strong wind from where you are toward the cliff."

	"There is. It's still uncomfortable, but we can stand more if we have to."

	"Just wait a while."

	The mate saw nothing else to do.

	Barlennan would have done the same, if the choice had been offered. Hars had worked the balloon rather jerkily downward from its ceiling until the basket was only a few yards above the tallest boulders, but at every level the wind was now toward the cliff edge. It was carrying them far too rapidly for a safe landing; hooking the car on a boulder and tipping the crew out was not acceptable. They could easily have fallen several body lengths. The cliff edge—or rather, the nearest point of the new slope—was less than half a mile away; much less, now. It seemed safest as well as unavoidable to go out beyond it and drop below the level of the plateau, a maneuver which should at least provide a wider choice of wind directions.

	It didn't. There still was only one choice, it turned out. A little later, after his quick physics lesson, Dondragmer could have told his captain what the choice would be, but the information would have been of little help.

	As Bree Three neared the top of the slope, the temperature rose abruptly, the balloon started upward, and the surroundings faded from sight.

	Neither the need nor the possibility of instrument flying had ever occurred to Barlennan or any of his crew. They had felt the upward surge, tiny as the acceleration was compared to the local gravity, and the captain could tell from the tracker readings that the climb was continuing. The instrument had been the first one salvaged from the very top of the rocket; its main purposes had been to help guide the original landing, with the additional hope that if the south pole were not found exactly its distance from the rocket could be determined and, possibly, seismic measurements be secured later. 

	To Barlennan, the temperature rise plus the upward acceleration suggested an upward air current heated from below and outside the balloon; Hars judged the same and reacted at once, slanting the vanes to waste hot air to the sides. The captain's first thought was that this was the proper reaction; then he realized that the climb couldn't possibly last long, but might very well take them above the balloon's normal ceiling. If the upward impulse ceased at some point, which it could hardly help doing, even full fire might not be enough to keep a catastrophic descent from following.

	"Keep it hot! Hot as you can!" he hooted. The fireman reversed the slope of the guides without question, though perhaps not without uneasiness. For several seconds the crew remained without reference points, though the figures on the instrument showed they were still climbing; then the surrounding fog began to thin, and sun and sky could once again be seen.

	The ground directly below could not, nor that along the former line of the cliff edge; they were still in fog. Toward the plateau, however, boulders were visible once more. In the opposite direction the less rugged area of the lowland showed fuzzily at first, but quickly cleared. Evidently they were still travelling in the same direction. A glance at the inertial reading confirmed this.

	The readout was reliable to fourteen places, even here; it had been made visible on the surface of the baseball-sized sphere to permit initial calibration, and Barlennan was not the only member of his crew to have learned to interpret the characters. Hexadecimal readings weren't too difficult for people who normally used base eight. The tracker was completely solid, with no moving parts larger than electrons, and the gravity had produced no readable change in its behavior, the Flyers had reported. It had, after all, been designed for such a field.

	It quickly became just as evident that the expected descent had started, and Hars, without further orders, heaped more fuel on the fires. Karondrasee sprinkled a contribution from his juice tank. Barlennan looked upward rather than at the approaching ground; wrinkling of the balloon fabric from rising pressure would mean more than the narrowing of the space still below them, however read. It occurred fleetingly to him that a small sealed balloon at regular temperature might serve as an even quicker method of determining rate of descent. One could watch it swell toward full or crumple toward flatness. 

	It would also be something they should be able to make themselves. There would be no other inertial instruments until they got back to the equator, where Flyers could land.

	But that could be thought out later, if he were alive to think about it. They were descending fast now, as even vision could tell when he glanced downward, but at least the skin was still smooth. The balloon was maintaining its volume in spite of the rising outside pressure; Hars was doing his job.

	The possibility of the bag's bursting during a climb had bothered the crews during the earliest flights, but the Flyers had assured them that the opening through which hot air entered it would never let the pressure get too high inside.

	Again fleetingly, Barlennan wondered whether they might be wrong again.

	They weren't, this time. The descent slowed and stopped, though it was fortunate they were no longer over the plateau. The cliff now was hidden by the same fog which had concealed the rest of the world on the upward surge, and the numbers said they were over a hundred feet lower than the rocket. At this point the voice of Jeanette, which had been surprisingly silent for the last few minutes, sounded again.

	"Captain, what's happened? Where are you? We can't see anything but the sort of ground across the river from the cliff, and it doesn't have enough features for any of us to recognize. We can read the tracker, but can't match figures with landscape yet. Can you turn the eye so we can see the cliff and the boulder country?"

	"Turning," Barlennan replied, gesturing Karondrasee toward the rotation lines. "I'm not sure, but I think we're pretty close to where the test was made, only we've passed the cliff. If it still is a cliff. Can your eye see through fog? If it can, you'll know better than I where we are when you look back. Where's Dondragmer? I should be able to—"

	"I can hear you, Captain. I can't make a very good report. The falling of the cliff stopped a couple of miles after it passed us, but we can't get back to where the ship was yet. It's too hot. The Flyers say that's to be expected, and at least the lower part of the fall is producing fog too dense to see through. Luckily the wind's now blowing toward the rockfall and keeping fog and heat away from us, but we can't get really near the ship yet."

	"Can you see enough to guess whether it escaped?"

	"No, sir. And if it's still uncovered it may not stay that way long. If you and the balloon were here you could tell better than we can, but it looks to us as though the very bottom of the fall were still moving this way. More like flowing than falling." 

	"I see the wind near the ground where we are is also moving toward the rocks, and now that you mention it, I think we can see that outward flow, too. We'll see it better when we get closer; we've let down pretty far—more honestly, we were pretty low when Hars killed our drop—and yes, we're blowing back toward the cliff now."

	The conversation had been in Stennish, but Parkos had been able to follow it.

	"Then you'd better climb again, Captain!" she cried. "If you're carried too close to the slope—well, I don't know how much heat you can stand, but you'll be cycling though that updraft again. You'll be starting from lower down, where it should be a lot hotter!"

	Hars spoke as he manipulated the guides, without waiting for orders. "Worse than that, Captain. I don't think we have enough fuel to manage another descent like this one. We'd better get up into the flow away from the plateau, get some more distance, and then land before we're carried back in again. The fog up there is blowing out past us the way we need to go, so there's a good wind not too far up." 

	Barlennan gestured assent to the fireman.

	"Don, you must have heard that. Unless something serious happens, we won't call you again until we're on the ground. You can tell me anything you think worthwhile. Jeanette, you must have had a good look at the fog yourself by now. Can you see through it?"

	"Probably no better than you. We can see the stuff lifting from the rocks at the edge of the slope; they must be pretty hot. Did you smell anything, familiar or otherwise, while you were in it? We're trying to guess what could be boiling."

	"There was some ammonia. Nothing else I could tell, but ordinary methane seems likely, too. How about the rest of you?" The others gestured negatively.

	"That's interesting just the same. Have you smelled any ammonia since you left the equatorial regions?"

	"No. Not that I can remember." Once more the others agreed with him.

	"It's hard to see how that stuff could be so far from the equator at this season," remarked another human voice. "I'd expect most of the planet's supply to be frozen in the other hemisphere right now."

	Once more the captain focused his attention on his more immediate problems. Hars had found the wind they needed and was holding altitude with his usual skill, and the line of fog was once more receding; but the fuel was getting very low indeed. It would not be good to let down into the other wind too early, of course; but if it took them too long to reach a safe distance, there might not be enough fire to make the descent and landing safely.

	"Your judgment, Hars," the captain said. "Get as far as you think will let us down without flattening us. Don't wait for my orders."

	The fireman gestured understanding without taking his attention from his levers. Barlennan had never learned to like situations where he wasn't in personal control, but he had long ago learned to be a captain. There were situations which didn't leave time for orders.

	In Barlennan's opinion, his pilot started the letdown too soon, but he said nothing. Hars almost certainly had a better idea of how much fuel the descent would take, and if the pilot was actually allowing a greater safety margin than the captain thought necessary, there was an excellent chance that he was right. Watching the balloon's still wrinkle-free skin seemed wiser than interfering. At least, any dents would appear near the bottom first.

	It had occurred long ago to one of the alien watchers that if the lower half of the balloon were to cave in sufficiently, the bag might serve as a fair parachute. She had then calculated the terminal velocity of the resulting system in the polar regions and decided not to mention the idea to anyone. The resulting ignorance spared the captain some worry.

	Barlennan was partly right; the descent had started too soon, from one point of view. They were in the grip of the cliffward wind well before they reached the ground. It might, however, be too late as well; the fuel was going rapidly. The natives were unfamiliar with alien literature and would probably never have thought of using part of their basket for the fuel. This was probably just as well, since anything which distracted Hars from his piloting would very probably have killed the four of them. As it was, they were saved almost certainly by the fact that something else was approaching from the direction of the cliff.

	It was not methane. At least, it certainly was not ocean-pure methane; it could barely be called a liquid. Slush or mud would be better words. It lay under them as the supporting heat dwindled below the ability of the guiding deflectors to keep the balloon contents hot enough.

	The first wrinkles appeared in the bag; Karondrasee's bellow of alarm just barely preceded contact between the basket and the semi-fluid. The car stopped almost at once, after a fall violent enough to make the stuff splash and jolt the occupants severely; the bag took rather longer to touch. The cordage tried to pull the basket toward the cliff as the wind still dragged at the balloon. For just a moment Barlennan thought the car would be tipped over and dump its fire, and had enough time to wonder what would happen when the latter met the whatever-it-was; then it appeared that there was enough weight stuck—frozen?—under their feet to hold them nearly level.

	They were more or less safe, it appeared, for the moment, but like Dondragmer they were uncomfortably warm.

	There seemed no practical way out of the basket for the moment; the stuff surrounding them appeared dangerously hot, and there was no way to tell yet whether this would get worse, or better, or remain unchanged, not that the last would be much help.

	The captain didn't bother to ask the Flyers anything.

	"Dondragmer, can you hear me?"

	"Yes, Captain."

	"Have you been able to get back near the ship?"

	"We're closer."

	"How's the heat? We're down, but are stuck in some sort of goo. There's a lot of ammonia smell, but it doesn't look much like ammonia."

	"That's happened here, too. It's what's keeping us from getting any closer to where the ship was. It looks and smells to me like the methane-ammonia slush we saw a good deal of where we wintered and met the Flyers, but that may be just a guess. If it's right, the ammonia should freeze after a while and sink and leave ordinary methane on top, which should soon be cool enough to swim in. The Flyers won't commit themselves either, but agree we should watch for clear liquid to show on top of the stuff."

	"I hadn't thought of that, but here we'll have to wait anyway. I hope we don't cook while we're still waiting."

	"Is your fire out? Or is there any chance of flying the Bree again?"

	"None, I'd say, unless we can get rid of whatever is stuck all over the bottom of the basket and must have kept us from tipping over when we hit. Maybe we should take a chance on putting the heater out. I've been a little uneasy about letting fire get near the stuff around us, or vice versa, because I thought that might burn too; but if you're right there won't be any trouble."

	"If I'm right. Pardon me for sounding like a Flyer, but I said I was guessing."

	"Now that you've reminded me, I'm guessing right along with you. In any case, it's getting warmer all the time here, and something has got to be done."

	"How about just going over the side, and seeing if being farther from your fire will be enough?"

	Barlennan did not answer at once. If such an experiment were to be tried, there was just one person who would have to go over first. He temporized briefly.

	"There's no sign of the stuff settling, where you are? No liquid on top?" 

	"No. If it's going to happen, it should be upstream where you are, first, I'd guess."

	"Is there any stream? There doesn't seem to be any flow here."

	"No. I suppose the fall blocked it."

	"But the methane from upriver should flow around, and even if the original bed was filled with rock the river should just be pushed out farther from the cliff than before."

	"Maybe it was," the mate answered thoughtfully. "Maybe that's the liquid part of this stuff. But if it is, I wonder where the ammonia came from?"

	"We're arguing like Flyers," the captain cut off the debate. "I'll reach over and find out how hot this stuff is."

	The caterpillarlike Mesklinite anatomy was not constructed for toe-dipping; Barlennan had to reach over the side with one end or the other of his body, and lower a set of pincers into the stuff. He chose to use his head end, for whatever help his eyes might give him.

	"Barlennan?" it was Jeanette's voice.

	"I hear you."

	"Are you all right, and is the tracker still working?"

	"We're uncomfortable but still alive. I haven't looked at the machine since we stopped. I don't suppose heat will hurt it, considering who made it. I'll shade it so I can see the figures and get a reading."

	"Whenever you can, please. There are people here who will have trouble breathing until they learn its condition, now that we know you're all right. Its reading here hasn't changed for some minutes now."

	Jeanette was not actually a skilled liar, but had some natural diplomatic ability. It seemed unlikely that the captain, just now, would be able to sympathize very well with people worrying more about the instrument's condition than his own.

	"That's reasonable," Barlennan concurred. "We've been stranded for some time now. Here's what I read." He pronounced the symbols carefully.

	"Good. That's what we have here. If it should change its reading, please let me know." 

	Another thought struck the captain. "Can you tell us whether the fall is still going on, upstream? Dondragmer says it stopped just below his location."

	"It did. We can see clearly with his communicator. I can't answer your question. You're practically at the pole, we're over the equator. The only reason we can see your area at all from here is atmospheric refraction, which doesn't help the image. Otherwise you'd be below our horizon. We'd have to send out another mapping rocket."

	"Do your people think that's worth doing? I'd be glad of any information I could get from that direction."

	"I'll ask." The Flyer's voice fell silent, and there seemed no more excuse for delay in testing the slush, if that's what it was.

	Gingerly, his head and a few inches of his body over the basket's gunwale, Barlennan reached a chela toward the nearly white stuff. The sun was low as always at this latitude and season. At the moment it was beyond cliff and fog, but there was plenty of light. He could feel some warmth from the surface of whatever-it-was, but it didn't seem as a bad as before.

	About like the inside of the balloon bag, which had been found to be bearable much earlier when control lines had tangled in flight.

	The stuff was soft, though it resisted a little when poked. Whether it would be firm enough to support his weight, and what would happen if it weren't, were still open questions. There was only one way to get answers that the captain could see. At least, only one which could preserve his self-respect; he could order one of the others to climb over. He didn't.

	The stuff did resemble the slush they had encountered near the equator, as the mate had said. It was uncomfortably but not dangerously warm. It did not support him until he had sunk perhaps a third of his body volume. His report, when he finally got back in the basket with the assistance of the others and a length of rope, paraphrased history for some of the human listeners.

	"Too soft to walk on, too hard to swim in. We're here for a while, but we can stand the heat. Have you tried it, Dondragmer?"

	"Yes, Captain. You describe it well. We think we can see the ship, but whatever it is is almost entirely immersed in the slush, and we can't be sure. If it is, it's well to this side of the fallen rocks."

	"Good. Find out for sure as quickly as possible."

	The mate acknowledged the order, which both knew to be superfluous.

	Half a day later, with the sun on their own side of the former cliff, nothing had been accomplished except testing the inertial tracker. This had been carried from one side of the basket to the other, and the change in readings on its surface and at the receivers on Toorey had remained in agreement. Barlennan was not surprised; from his point of view nothing at all violent had happened during the wrecking of Bree Three.

The slush was still slush. This surprised the Flyers, who seemed to feel that if anything were going to settle at all it should do it pretty quickly on Mesklin; Barlennan had no basis for an opinion, though he certainly wished that something would happen.

	Fog was still rising from the slope a few hundred feet away. The Flyer prediction that the wind should cool the fallen rock fairly quickly seemed to have been another mistake. Barlennan didn't raise the subject; he was quite sure that the beings would point out that they hadn't actually specified a time numerically. This was quite true, and qualifed as an excuse even by the captain's standards.

	There had been, twice, sounds from inside the fog suggesting that rocks had moved, and the four people in the basket were alert for anything more of the sort. Dondragmer's people had heard nothing like it, the mate reported; but they, too, were listening. Anything like that should happen upstream first, each told himself. This was not mentioned aloud.

	The fire had not been extinguished after the captain's experiment, but was now dead for lack of fuel. There were plenty of Mesklin's scraggy plants in sight in various directions on the shore beyond the slush, but there was no way to reach them; and there seemed not to be enough of them to get Bree Three into the air again in any case. Karondrasee had plenty of meat juice in his tank, but there seemed no way to use it.

	It was two whole days before anything noteworthy happened, and its development then was gradual.

	There were more of the falling-rock sounds. Nothing could be seen; the fog, if anything, was thicker, and the Breeze toward the rubble slope somewhat faster.

	Then another quite familiar sound made itself heard.

	"Captain! A current! Flowing—" Hars uttered the words very softly for a Mesklinite, though Jeanette had no trouble hearing him. She heard the trickling of liquid, too, since the pilot had been doing his best not to drown it out with his own voice.

	"Which way? Can any of you tell?" she asked. Barlennan couldn't decide himself; the sound had seemed to come first from the direction of the rocks, then from what had been upstream, then from many directions at once. The most convincing came from the fog.

	Flowing liquid? Methane? Was the ammonia, if that's what it was, finally starting to settle?

	Methane, yes. Settling ammonia, apparently not. Motion caught the eyes of the four crewmen in several directions almost at once. Most of it was from cliffward and upstream, but Barlennan caught sight of a trickle which seemed to rise from almost under the basket, a rivulet which spread, and grew, and flowed downriver as he watched. Others appeared and behaved the same way, more and more, minute after minute; then quite suddenly, they vanished in a single spreading sheet of liquid which the crew now realized covered much of the landscape in the upstream direction. It was as though the river had resumed flowing, and was coming up through the slush, and making a new bed for itself beyond the tumbled rocks which had filled the old one.

	It was methane, as taste promptly proved—it was not a laboratory situation to the Mesklinites, who were by now pretty thirsty anyway. The river was being reborn.

	Yes, reborn. There was plenty of liquid coming from upstream, but there was nearly as much—perhaps more—welling up from under the slush and from the direction of the rocks.

	The basket began to move, as Jeanette promptly reported.

	"We know," the captain replied tersely.

	"Will you float?" asked the Flyer.

	"We should. The basket's made of wood—real wood, not that funny stuff from the ammonia flats. What we need to know is whether it'll float level. We didn't worry that much about weight distribution when we made it."

	"How about the bag?"

	"That's another question. We may have to cut it free. Depends whether it acts more like a sea anchor or a sail. Dondragmer, we must be heading your way. I can't guess how long we'll be getting there."

	"We're watching, Captain. If you have to free the bag, we'll try to capture it, and you of course. The slush is still slush down here, but we're watching for liquid, too. If the thing we think is the ship starts to move, I'll take swimmers to do what we can."

	"Good. We're going to be busy here, but one of us will keep in touch. If you don't hear from us for more than a few seconds, you'll know something we didn't expect has happened. In that case, send some people up this way to give any help they can. We're going faster, I think. The bag is dragging behind us, whether it's touching bottom or feeling wind I don't know. Probably wind, I think; there's an upstream component to that now, and the bag itself is pulling a little toward the fog. It's pulling us that way too."

	"Hadn't you better cut loose, then, Captain?"

	"Not until we can see whether moving in toward the rock is good or bad. We're standing by to cut if we have to. There doesn't seem to be anything yet for us to hit."

	Barlennan kept a running commentary going, as he had promised, while basket and bag headed downstream. The nearest motionless objects were now either too distant—features on the land away from the cliff—or too vague, like the fog, to allow a trustworthy estimate of speed. It was one of the Flyers who pointed out that the tracker was moving downstream surprisingly fast. He didn't seem really sure that it was surprising; all earlier estimates of the river current had come from direction measurements of the communicator outputs, which were not very reliable with the line of sight to the moon practically horizontal. This was not the tracker's first trip to the lower ground, but was its first ride on what had become a surface vehicle.

	One of the watchers remarked audibly that he was surprised the vehicle wasn't in white water; another, not bothering to correct the name of the liquid, suggested that the first speaker think gravity. Just what would "white" imply about the current's speed on Mesklin?

	The twelve-plus kilometers an hour was several times any earlier estimate, however unreliable that might have been. It implied a source of liquid unrelated to what had been seen of the upstream areas from earlier balloon flights. This was not merely methane which had found its way, after some delay, around the recent rockfall.

	The people on the basket finally observed this, too. The drag toward the rocks had been maintained as wind kept its grip on the now rapidly flattening bag. The sharp rocks were suddenly passing uncomfortably close to a structure which had been designed for lightness. Contact could be awkward even if the pieces continued to float, as they no doubt would. Barlennan heard himself commenting on this as part of his running report, and interrupted the monologue with a sudden, sharp order.

	"All of you! Cut it free!"

	Simultaneously the bag caught on a sharp, solid rock corner, jerking the basket to a halt; anywhere near the equator the crew would have been hurled overboard. Karondrasee, in fact, did get jerked over the side.

	For just a moment the cook could be seen borne away from the suddenly anchored car; then, as the others finished cutting the dozen cords which had held basket and bag together, the former resumed its downstream rush even more rapidly than before. It was now relatively motionless with respect to the swimmer, and he had no trouble wriggling back to what might or might not be safety. He needed no help getting aboard through one of the gunwale crenelations, and the fact that he brought a good deal of methane with him made no real difference. In spite of the total absence of spray, the footing on board was already extremely wet. During the brief halt, the river had spilled over the upstream gunwale and nearly washed several more objects into the river.

	The communicator was high enough above the deck to stay clear, but the inertial tracker was not. Neither were the three remaining natives. It was Hars, perhaps more concerned with all things connected with flying, who curled his long body about the sphere, gripping it with every leg which could be brought to the task. Sailor and instrument washed rapidly across the deck in the direction from which Karondrasee was swimming, but they did not go overboard.

	Hars' own display of personal strength surprised no one, but his fellows and the watching Flyers were all rather startled that the gunwale seized by one of his chelae did not tear loose from the rest of the basket. He uncoiled partly, still retaining his grip on the tracker, and spread the load on the gunwale with more pincers; by the time the cook was safely aboard, the sloshing of liquid across the deck had ceased and the tension had eased.

	"It would have been easy enough to find," Barlennan remarked. "I know it would have sunk, but the river's pretty clear."

	"Is the bottom solid?" a Flyer voice—again, not Jeanette's—asked pointedly.

	"I don't know, but it looks—" The captain paused, then went on, "Just a moment." He vanished over the rail. His crew watched with interest but no great concern; the aliens were highly concerned but couldn't watch. The long body reappeared and moved in front of the lens.

	"It might have been serious at that. It's the same slushy stuff, and it's travelling—not as fast as the river, but if the tracker had sunk we'd never have found it. Good work, Hars." The exhaled breaths were audible through the communicator, but carried no meaning to the natives.

	Dondragmer could not see anything nor hear everything, but had been able to infer what was happening.

	"Is anyone watching ahead, Captain? You must be travelling pretty fast. We're getting ourselves and the radio back from the river; it seems from what you said it's a lot wider and faster where you are now, and that it became so very suddenly. All of us are staying with the radio as we move it; I'm sure the Flyers know that faster-moving methane carries things more easily."

	"Sixth-power law," a barely audible alien voice muttered. The words were not in Stennish, but the mate understood both them and their mathematical implications. Barlennan got the former only, but no order was needed to drive the mate to greater haste. The captain had heard the question about looking ahead, and without acknowledging the words was doing so.

	Actually, looking aside was more worrisome; the basket was still closer than he liked to the edge of the rockfall.

	Worse—much worse—it could be seen that much of the finer waste from the cliff was being washed away by the current, leaving widening spaces between the larger fragments.

	Well, the Flyers weren't always wrong, of course.

	He could not see what was happening to the loosened stuff. The surface was too turbulent to offer a clear view below it.

	He remembered his earlier promise and began describing the new phenomenon to Dondragmer. Sherrer, his flexible body partly overside, rotated the basket to let the communicator eye look ahead. His chelae were poorly shaped for the work, but his paddling did have results.

	"You seem to be approaching a bend to the right, in both fog and river," Jeanette remarked. "I'd guess it's that kink—that point—in what used to be the cliff, a couple of miles or so upstream from where Don is."

	Barlennan saw no reason to disagree, and the possibilities which a quick change in flow might offer were enough to focus his attention. "Dondragmer, is your part of the river widening at all rapidly? It should be if the Flyer's right. How well are you moving the radio? Can you keep it moving and also let it look upstream?"

	"We are moving. I'm not sure about change in width, since we're away from the river itself now. We're keeping the lens pointed more or less upstream, but I'm afraid they're not getting a very steady view."

	"Don't worry about that, Don. We can take pix when it's steady and look at them. You're right about keeping the viewer as safe as possible."

	"Thank you, Flyer Jeanette."

	It was indeed a turn to the right, the captain saw as they approached it. The current was visibly swifter; they were still close enough to the shattered. pulverized, and steaming rocks for this to be very obvious. 

	He suddenly realized that everything at the foot of the pile was much larger now; the fragments resembled the gigantic—to him—slabs and prisms which had earlier shown only on the higher and steeper part of the fall.

	It was hard to tell from this close, but the general slope seemed to be steeper, too, as though the whole fallen mass were still gently sinking.

	Maybe it was. The fine stuff below was certainly vanishing.

	There was a fan of standing ripples angling out across their course ahead; the mate would almost certainly have been curious about this, but Barlennan was just uneasy. The river was still liquid. He felt it again to make sure. He did not, however, wonder what made these little ridges in it—only what would happen to the basket and its passengers when they reached them.

	Which they would do in seconds. Would they be hitting liquid, or something solid enough to support those humps which lay a little above the general river level, or something slippery which would bend the raft's structure into its own shape?

	It was liquid, both its high and its low parts, they found. Motionless waves were something new to Barlennan, and he reported as well as he could to his mate and the aliens. The basket was still intact, though everyone aboard had felt the deck under his feet follow the up-and-down displacement of the surface as they passed the still ripples. The Flyers seemed unsurprised, but Barlennan was not asking for explanations just yet.

	The foursome ceased thinking about the ripples at once. The next event was prompt, less unfamiliar, and more frightening.

	There was an eddy on the downstream side of the point, where the liquid swept around. They had all seen such things before, but never in gravity this high. If there had been time to think, they might have foreseen this one, though not in full detail. They had never, after all, felt one in gravity this high either.

	Barlennan tried to keep reporting.

	"We're around the corner. We can't see you, though—"

	"I haven't seen you, either."

	"Not surprising. There's a hollow in the methane, we're quite a bit below the river level, and can't see much but the rocks—when we're looking that way."

	"Captain! What's happening? The eye and the tracker both say you're—you're moving in a tight circle. How can—?"

	It was often nice to have the Flyers tell him what was going on and advise him what to do about it. It was sometimes nice to have them unable to tell him what was going on, thus providing a little salting to the flavor of omniscience they claimed not to want. It was not nice when he didn't know what to do about it himself. He described what was happening in as much detail as he could observe, and as he did so realized what was probably going to happen next.

	The broad swirl of liquid cut in toward the edge of the rock slope and divided there, some swerving back upstream and some resuming its original journey down. At the point where the division occurred, the biggest rocks were visibly settling still. Not fast, but visibly. The finer stuff had washed out from between and among them, and the higher and larger items were crowding vertically closer to each other as the material originally separating them vanished.

	The pieces were big. They were very big, and as the seconds brought the basket closer the face the slope began to change. It grew still steeper, and the spaces between the huge boulders seemed to open like mouths, leading into the face of the bank—with throats leading under it.

	All four sailors were familiar with the hazard of striking rocks. They had even, occasionally, been swept between rocks.

	But they were Mesklinites, and if any of their colleagues had ever been carried under rocks no one had ever heard about it.

	The four paddled frantically but without much result, even after the captain got them all paddling in the same direction. The basket flung itself toward the bank, swerving only at the last moment, with some of the huge fragments close enough for even the Mesklinites to touch.

	The swerve was upstream, back toward the point, which meant that they would be going through it all again. And perhaps again, and again . . . 

	The rocks were still quite hot, though the wind toward the rocky bank made things a little better. Methane striking the fragments didn't actually splash, though it did rise a short distance above its regular level before boiling into invisibility and reappearing as fog. Spray was extremely rare this far from the equator.

	They reached the upstream side of the eddy, swept out into the main current once more, but were not yet free. It was going to be again.

	But only once. They were carried back toward the fallen cliff somewhat farther downstream this time. The settling was still going on, but less rapidly; could one hope it was actually stopping? That the mud was nearly all gone, and the big fragments resting directly on each other? Well, yes, one could hope. There were no sounds of falling and grinding, after all. 

	The lowest part of the rockpile was now definitely much steeper and formed of really huge fragments, with open spaces between sometimes wide enough for one of the old Bree's rafts; and the current was not dividing at the very edge any more. Methane was flowing into the interstices, flowing almost as rapidly as in the farther-out parts of the eddy. There was no way to paddle the basket fast enough and far enough either up or downstream to get it carried in either direction. It was going to travel into the wreckage of the cliff.

	Not even the Flyers could find words. They could see it coming; their lens at the moment was pointing in the basket's direction of motion. None of them ever admitted whether the fate of the natives or the loss of the communicator and tracker concerned them more.

	There were other communicators, of course, and Dondragmer might prove to be a better agent than his captain; but there was only the one tracker, and great things had been planned for it once it had been found to be still functional. If it could be carried over land and sea all the way back to the equator, while being followed from above by communicator waves so that gravity and inertial effects could be distinguished, what couldn't be learned of Mesklin's interior?

	No one had yet discussed this project with Barlennan, and in any case it would not have been the captain's primary concern just now. He and his men were being washed underground, on what amounted to a patch of driftwood. It was much, much later before any of them realized how lucky it was that the sun was ahead of them, on the high side of the cliff, just then.

	It grew relatively dark the moment they had rock nearly surrounding them, with only a modest illumination from the sunlit ground across the river. Their heads and eye turned back toward the light, and stayed there as the view narrowed; and before they really saw and could respond to the unimaginable tonnage of material suddenly above them, the darkness was complete except for the faint glow of the tracker's numbers.

	The Flyers, Barlennan thought after a moment, should have commented on the darkness or the fact that the tracker was still indicating motion or something, but the communicator was silent. It remained so after several hopeful calls by the captain.

	It had never occurred to him that whatever carried the messages to and from Toorey might be blocked by intervening rock. The concept of a completely surrounding bed of intervening anything had never crossed his mind.

	For a moment he managed to concentrate on all he could see. The digits on the tracker screen agreed with his own sensations; they were speeding up, slowing down, jerking from side to side—the basket was in fact still being carried by a current, which was weaving its way around things. He should have been able to tell which way and how far, from the tracker readings; should, indeed, have been able to retrace their path if he had had any control of their motion. The general direction was indeed obvious; they were heading deeper under the former cliff. How far under was another matter; he didn't remember the position reading when they had gone into the dark, and the succession of numbers which had followed that moment had been too complex to memorize.

	It was never clear to any of them later how they were able to keep thinking—why the four of them didn't succumb at once to total panic. The Flyers commented later how fortunate it was that all four had had balloon experience, but it was not clear to Barlennan why that should help them with the concept of heavy material overhead. He tended to credit his own retention of sanity to his profession. He was a captain, he was responsible, he was used to doing whatever he could that was called for at the moment, and leaving what he couldn't control to luck. This may have corresponded to an almost human personal arrogance. Even so, every little while—he had no way of telling how often—the thought of what he was under threatened to crowd his attention away from everything else. 

	Anything to take that awareness away from him would have helped. He would even have welcomed a theoretical argument from the Flyers. Why all this open space under the cliff, or where the cliff had been? How much mud had there been to wash away, and how had it vanished this quickly so far from the actual river? Or had it? How far did the open space extend? Up and down, probably not very; they were still floating, and it was hard to imagine how the methane surface could have gotten either above the river outside or very far below it. That inspiration caused him to focus on the vertical readings of the tracker for a while; he found that their height was indeed almost constant.

	But liquid flows downhill, and this was flowing, so there must be at least a small drop. There might be a big one farther ahead; this didn't seem very good to think of either.

	How deep was it? What were their chances of grounding—and staying there in the dark with too much of the world overhead? He thought of trying to find out by swimming, but could imagine no way for a swimmer to find the basket again. He realized later what his failure to think of safety ropes must have implied about his state of mind.

	They could call to each other, of course; he tried that.

	Multiple echoes responded to his hoots and made sound direction meaningless. In a way this was comforting; Mesklin's stratosphere started only a few hundred meters above the general surface at this latitude. The air, after cooling for a very short distance upward, began to rise in temperature with increasing altitude, so that sounds originating at one spot refracted downward again before going too far. Complex echo patterns from sounds of distant origin were standard, and these gave a slight—very slight—suggestion of clear air above. They actually fooled Karondrasee, who asked, "Captain! It's got to be open above after all! Why is it so dark?"

	The captain was quick enough to reply that he didn't know, and almost as quickly inspired to ask, "See if you can think of an answer before the Flyers tell us." That should provide something to distract all the others.

	Hars, though, seemed somehow able to think coherently, at least for the moment.

	"Captain, shouldn't we do something to secure the instruments? We could run aground any time, though we do seem to be getting carried around things so far, and we don't know how hard we'd strike. The radio isn't any good to us right now, but the tracker might make a lot of difference. if it went overboard I don't see how we'd ever get back out."

	"Right. I don't see how we can manage that anyway until the current lets us go, but secure them just the same. The radio will be easy enough; it was made to be fastened to things. The tracker wasn't, though. All of you try to think of a hitch or something to hold it fast."

	"Why did they make it ball-shaped?" Even Sherrer sounded more annoyed than afraid. "Didn't they ever think of having to keep it from falling overboard?"

	Barlennan could think of no useful answer. he had a fairly clear idea of where the rocket had traveled, but no real notion of ballistics. "Salvage all the cordage you can find," was all he said. "Coil it up and stow it around your bodies. Hars, stay with the tracker and hold onto it as well as you can until we solve the tie-down problem. Think of this as a doldrum situation. We do what we can to make use of wind, or current, or an animal we can harpoon to tow us, and hope that one or another of them will happen. Only this time we have a whole new list of things we need to be ready for, and don't know anything on the list."

	Shouldn't we perhaps moor to something, Captain?" asked Sherrer. "The tracker says we're getting farther from the river all the time. The farther we travel, the farther we'll have to go to get back."

	"If you can find a way to moor us, I'll agree. Personally I can't see what we're passing."

	"Of course we can't see, but we can reach out to feel. Surely some of the broken cliff must be rough enough for a grip!"

	"For a grip, maybe. For a rope? Well, reach out and learn what you can." The sailor presumably obeyed, but made no report for a long time.

	Nothing particular happened during that time—whether a day or an hour none of them could tell. Cordage was found and secured. Hars contrived a spherical, close-meshed net of some of the finer lines, and enclosed the tracker in this. Without commenting to the captain, he secured it to his own body. Like the rest, he had a strong feeling that this device, if anything, was most likely to get them back to daylight.

	Again, Barlennan began wishing for Flyer theories and arguments. He found himself even thinking along Flyer lines. Why was there liquid so far under what had been a layer of solid rock hundreds of feet thick? The fact that the rock was no longer solid did not explain where the liquid filling the new space could be coming from. Why was there any place away from the original river for it to flow to? (Item not to think of: liquid flows downhill; where were they being carried?) Why had the finer material been washed, or carried somehow, away from the really large fragments of rock, even in here apparently turning the whole fallen area into a random stack of slabs and columns long enough and wide enough, as it had seemed from their last glimpses outside, to enclose more empty space than rock? Where had the fine stuff gone? (Well, downstream, obviously.) Where had the medium-sized stuff gone? (No obvious answer.)

	Why did they all seem to be sane in a situation which should have driven any normal person out of his mind? (Or were they? No, Captain, keep away from that thought, too.) They were, after all, experienced and competent members of a dangerous situation offered a good chance of getting something worthwhile out of it. (And of course a better one of not living to enjoy the profit.) That last thought had been banished from all their minds years before, of course. They were still alive; therefore they were lucky.

	Where had the underpinnings of the plateau gone, actually? That was a real Flyer question. And the Flyers were in no position to answer it.

	They would want to know the answer, though. And Barlennan and his people were the only ones likely to provide one.

	That was a thought to bolster sanity. The Flyers always wanted information.

	Sherrer was having more trouble. His sounds, when he made any at all, were less and less understandable words and more and more short howls of terror. When words could be made out, they were ones that only magnified the fear.

	"The world is up there... it's heavy... what can keep it from falling? We're..."

	"Quiet!" snapped the captain. "Why should it fall? It hasn't yet, and..." his voice trailed off. The stuff above, after all, hadn't had that much time to finish the settling it seemed to have started. It could quite easily be getting ready to fall farther. And it was indeed heavy. There was no way of convincing themselves they were back near the equator, were a healthy person could lift rocks like that. No way, even if they couldn't see. Stop catching Sherrer's fears, Captain...

	Even if they couldn't see...

	He jerked out another order; his own mind was recovering, it seemed. "Sherrer, bend a good line around yourself, at least twenty body lengths, and make sure is other end is secure to the basket—to some really strong part of the basket. Then go overboard carefully and try to find how deep it is, and whether there is anything we could moor to. Don't leave too much slack; keep most of it coiled against you and stay close to us at first."

	"Yes, sir." Barlennan listened anxiously; giving the fellow something to occupy his mind was one thing, putting him where he wouldn't expect to see upward might be even better. the information would be useful, of course, but the action might keep the fellow from complete panic.

	The liquid was quiet; they were moving with it, not through it, and the sound as it slid around the rocks which must be there was hardly audible. The other three could hear as Sherrer measured his line, secured it at both ends, and slipped overboard. Without order, Hars gripped the inboard end of the cord with a holding nipper.

	"He's pulling away a bit, Captain; I don't suppose he can see to keep near us. I'll give him a tug or two to let him know." Barlennan didn't bother to answer. "There's some slack, now. What pull there is is smooth; he can't have met anything solid."

	Sherrer's voice abruptly sounded, muffled by the methane-air interface but quite audible. The Mesklinite vocal apparatus, a modified part of their ancestors' swimming siphons, worked impressively well in both media. "We're going a little better than walking speed, Captain. I'm on the bottom. It seems to be that slush rather than rock most of the time, thought I hit something solid every little while. Shall I try to slow the basket, if I can get a good grip on anything?" The sailor seemed perfectly calm now.

	"Try, but not too hard; if you get pulled free by the basket, don't fight it," replied Barlennan.

	"Yes, sir. The liquid's getting shallower, I think."

	There was no more after that to be said; the sailor had been right about decreasing depth. Moments later, everyone still in the basket recognized the sensation as their craft ran aground on an oozy surface. Instantly the captain snapped further orders.

	"You two—lines on yourselves and go overside. Get away from here in different directions. Use voice softly to keep yourselves apart—no echoes if you can help it. Find out everything there is around here, out as fast as your lines will allow. If there is anything we can moor to, report at once and then start doing it."

	He was obeyed promptly, and submerged hoots and howls began to echo around the basket. There were, it turned out, plenty of rocks projecting from the ammonia-smelling ooze; some of them barely broke the surface of the methane, many extended upward farther than the sailors could reach. In less than half a day, as well as anyone could guess, they were moored solidly to five different bases, two of them too high to flip a noose over. At least they shouldn't get any farther from the outside.

	Getting back to it might be rather different.

	All three of the sailors who had been overboard sounded easier in their minds. The captain wasn't sure whether this could be attributed to lack of upward vision, or just to being occupied; but there was a way to test.

	He groped his way to the now cold fire box—cold only in comparison to its working state; the surroundings still felt like the inside of the balloon bag in flight—and felt for the control baffles which had directed the lifting air. These were made of the same fabric as the bag itself, stretched on light wooden frames. Carefully he nipped out a section of the material and deliberately spread it over his head and eyes.

	The only obvious difference was that he could no longer see the tracker’s characters. He felt no easier about what lay overhead.

	But then, that hadn’t bothered him, the captain, as much before as he thought it should have. A better subject was needed, though Barlennan had never heard of guinea pigs.

	"Sherrer! Come aboard."

	"Yes, Captain." If the sailor were uneasy, his voice failed to betray the fact. He came over the side in a few seconds, presumably coiling his safety line as he came.

	"Here, sir."

	"Can you think of any way back?"

	"No, sir. We’re—we’re underneath—" The voice trembled.

	"Don’t be ashamed of being scared. It would probably mean something worse if you weren’t. Did you feel better while you were working just now?"

	"Yes, Captain."

	"Feel the piece of sail cloth I’m holding here."

	"I have it, sir."

	"Put it over your head and eyes, like this." Barlennan helped. "Find some thin line and tie it there. Then go back overboard, and check the bottom all around us for small rocks. I think we can use some—as many as you can find."

	Sherrer was neither stupid nor unimaginative, but was not the sort to ask anything like "How?" to an order. He simply obeyed. Barlennan was satisfied. He didn’t want rocks, he wanted information, and would have had a hard time in answering a "how" or a "why" just then. The Flyers had not taught him any psychology but his profession had; and he had grasped certain principles of research—not as well as his mate, but better than vaguely. Sherrer obviously shouldn’t know in advance what was expected—or rather, hoped. Let him look for rocks for half a day or so, and then come aboard with them, and give him something else to do with the hood still over his eyes. Something not too demanding of his attention— But how about Barlennan’s own attention? Captain or not, there were moments when the tonnage above seemed to fill his mind. There was nothing else to think of. Nothing else in the world. Maybe he’d better make another hood for himself.

	No. He was the captain, and he knew what was up there. If anyone could ignore it without special help, he should be the one.

	Of course, it would be nice if something else were to get his attention away from the World Above.

	It was, indeed, a relief when something did.

	Jeanette had spent several minutes calling Barlennan after his communicator had gone silent and dark. She had his verbal reports up to that time, and wasn’t very hopeful after it; the fadeout hadn’t been quite instantaneous. The drifters hadn’t hit anything hard and suddenly, up to the time sound and picture had faded. The waves the communicators used were long enough to reach their goal by diffraction even when Toorey was on the far side of the cliff from the Bree’s crew, so the basket must have been pretty well surrounded by some obstacle within a second or two after that. Barlennan had reported that the methane was flowing into openings in the rock fall; she had seen this, as well.

	And Jeanette had as clear an idea as any human being possibly could of what being inside a cave or a tunnel at "normal" gravity must mean to a Mesklinite.

	She switched to Dondragmer’s set at once. He also had heard his captain’s messages, delayed barely a second by the round trip to Toorey, and had as clear an idea as the Flyer of what had happened. Some of his sailors had already been ordered downstream to investigate the end of the rock fall; after a moment’s thought, he let them go on. He split the remainder into two groups, sending one up toward the point where the eddy had presumably caused all the trouble and keeping the rest with him to get as close as possible as quickly as possible to where he was now pretty sure the original Bree was stranded.

	The stream had started to widen now as the captain had reported earlier from his upstream position, but the methane at the edge away from the plateau was not uncomfortably warm. Maybe they could reach the ship, or what they hoped was the ship, without getting scalded. The mate told the Flyers what he was doing, and led the way. The river was widening, its edge coming to meet them. The radio remained behind; swimming with it was not an option, and walking on the bottom with it seemed inadvisable. ‘Whoever carried it would be able to talk to the others and report to Toorey, but its viewing equipment would be useless unless it could be held above the surface. It seemed better to learn what could be found out, and then come back for the communicator. No one on the moon was pleased, but no one argued.

	The bottom was ordinary ground at first. It had been dry land since long before the Bree’s arrival, presumably; the liquid methane was spreading wider and wider past its former bank, and there had been little change in the volume of flow in the thousands of days since their first arrival.

	There was presumably little change now; the overflow represented liquid displaced from its former bed by rock.

	The crew waded for a while, then had to swim, watching where they were headed part of the time but checking below the surface frequently. They were something like halfway to where the ship seemed to be when the bottom began to show lighter in color, and closer examination showed that it was now the same ammonia slush reported earlier by the captain’s quartet. It was being washed downstream, they could see at first; then it covered the bottom with a uniform sheet of white, and its motion couldn’t be seen. Physical contact indicated that it was still moving.

	The methane was getting deeper, and Dondragmer kept a close eye on what he was now almost certain was the Bree. It had been hauled well ashore, but was now out in the stream—or rather, the stream had spread well past it. It would have to be floating soon. Perhaps it was floating now, the mate realized; they were all swimming, and would be carried downstream at the same rate, and the slope across the river was completely hidden by fog, so it was not easy to tell who or what was moving.

	It was the ship. It was afloat. It was easy to reach, fortunately; but it was not merely drifting along with the swimmers. The wind was toward the rock fall here, too, and the Bree was being carried very slowly toward the slope as the balloon basket had done.

	For just a moment the mate thought of making sail; then he realized that the wind was toward the rocks and the depth too shallow to lower centerboards and sail effectively across it. With only ten men aboard, rowing would be futile.

	Almost futile. Maybe they could keep her away from the rocks long enough to get the radio back aboard—no, they were already leaving that equipment upstream. Dondragmer ordered four of his crew back overboard.

	"Get the radio, and start taking it downstream. We’re not very far from the end of the rock fall, now; maybe when we get there the heat will ease off and the wind change. If it doesn’t, well, the ship’s a lot bigger than the balloon basket, and we may be able to paddle it so the rafts catch in a space too narrow to let us through."

	The crewmen obeyed. One of those remaining behind raised another point.

	"Will the rafts hold together if we catch her across a passage that way?"

	"I don’t know. Do any extra lashing you can between the outboard rafts before we hit. There aren’t enough of us to keep her off, we’ll soon be in the fog, and it can’t be far from there to the rocks—it seems to be formed by methane hitting them and boiling. I’m surprised the wind doesn’t let us see the edge of the fall; the captain could, further up."

	The ship had enough cordage to keep them all busy for the next few minutes. The mate saw his swimming party reach shore and head back upstream to where he could still see the communicator. The downstream party was still in sight as well. The river seemed to be growing even wider there, but its members were staying ashore for faster travel.

	The mate had time to think as he lashed. His thoughts rather paralleled the captain’s; where did all this methane come from? Unlike Barlennan, he came up with a plausible explanation.

	The original river had been fairly deep. If it had been well filled with fallen rock, it would have to spread over more ground, or travel faster, or both. But this idea, as the Flyers had often warned was likely to be the case, gave rise to more questions.

	If the methane were being displaced by the rocks, why was it flowing toward them? There was at the moment no way to ask the customers and, of course, no certainty that they would be able to answer. He would have to do more thinking himself

	And just now there was no time to do that. They were into the fog.

	Dondragmer silently berated himself for leaving to chance something he might have controlled. Even the few men now on board could have paddled to turn the cluster of rafts so that its longer side was toward the rocks, and thus improve its chance of catching rather than being swept between rocks and out of daylight and under— He hadn’t been thinking of under. Deliberately.

	Luck had been with them, as it turned out, but the mate still felt stupid. They didn’t touch sidewise, but the starboard bow raft of the cluster hit first on a rock barely above the surface. The after portion swung counterclockwise as the current kept pushing inward. The aft starboard raft struck, harder than anyone liked, on a huge slab which tilted up out of sight in the fog. The midships section continued to push shoreward briefly, but one aspect of the ship’s basic design proved its salvation. Ropes stretched, rafts along the starboard side heaved, and the Bree came to rest with bow and stern pressed firmly against equally firm rocks and with another fragment of the fall under her just forward of amidships. While the rocks stayed there, so would the Bree. At the moment, with the darkness farther in easily visible even with the fog, this was a relief

	Dondragmer gave no one time to think. He ordered one of the men overboard with the longest light line aboard.

	"Bend this around you. We’ll fasten the other end to the ship. Get to the bottom and start shoreward, taking the line with you. Try not to get washed downstream. If you run out of line before you reach shore—you probably will—surface and try to spot landmarks which will let you know where you are and how far downstream we’ve traveled. Then do your best

	to keep there and yell for the others. We should still be in hearing for them. If you make contact, tell them to bring the radio as close to this place as they can."

	"All right," the sailor affirmed, "but couldn’t someone start calling from where we are? Then they could be looking for me and have the spot marked a lot better when they see me.

	"Good. Right. We’ll do that. Over with you; they’ll still have to see you; they certainly won’t see us."

	The crewman vanished with no more words.

	The line paid out slowly, occasionally going slack for a moment. Dondragmer suspected that the sailor was occasionally losing contact with the bottom, a forgivable offense since the Mesklinite body averaged just barely denser than liquid methane and there was certainly a current. He didn’t want to ask, since one of his other men was, in response to orders, hooting as loudly as he could to get the attention of the downstream party. The mate concentrated on keeping track of the length of line paid out.

	This eventually reached its end. Rather than have it jerked from his grip and possibly even from the rail to which it had been secured, the mate tightened his own grip and began gently tugging as the end approached. An answering set of tugs came almost at once, and the sailor’s voice was audible between the bellows from the Bree’s deck.

	"Located, sir. I’m only about a hundred lengths or a little more from shore. I’m off the slush, and there’s plant stuff here I could tie the line to, but I want to make sure it’s solid first."

	"Right. Carry on. I’m sure you can hear Felmethes calling. Can you see the others? Can you tell whether they hear him?"

	"Can’t see them, sir, but I think I can hear them. Can’t you?" Dondragmer gestured to Felmethes to be silent for a moment. The fellow had, of course, been pausing to listen for answers at regular intervals, but was glad enough to wait a little longer.

	After a few seconds a long roar that seemed like a Mesklinite voice was audible, but no words could be distinguished. The sound ended eventually, and Dondragmer called to Kentherrer at the other end of the line.

	"Could you hear that? Could you understand them?"

	"Yes, sir. They keep asking if it’s you, and say they can’t understand you. There must be something about echoes along the rock faces."

	"Could be. See if you can make them understand you. If so, tell them what’s happened, and have them come back here."

	A perfectly comprehensible pattern of hoots in Kentherrer’s voice was the response; evidently he was more or less in touch with the other party but having trouble with clear communication. Dondragmer was patient. He was not exactly worried about the captain; there was very little hope that he and his fellows were alive, and rather less that they were sane. It was better not to rush into anything until there was at least a vague idea of where to rush.

	Besides, it was not likely that anything at all could be done about the missing balloonists until the Bree could be brought ashore and rigged again. Even then, it was far from clear just what could be done. The most obvious technique, searching among and under the fallen rocks, was unpromising even if there were some way of telling where to start the search.

	Come to think of it, there was a way for that. Barlennan had described in a good deal of detail the area downstream from the point where the eddy started. The point should still be there, and maybe even the eddy. If necessary, they could leave the ship where she was and search as a climbing or a swimming party.

	Under the rocks? Well, maybe.

	Kentherrer’s voice had faded, but could still just barely be heard. The party must be coming back. It seemed to the mate better to wait until they arrived, rather than attempt a three-cornered conversation through the echoes.

	He felt just a little foolish when Felmethes went overboard and began talking in an ordinary voice, submerged, first to Kentherrer and then, only a little louder, to the downstream party. He hadn’t heard, or at least distinguished, the message from the latter saying that they were going to submerge; but that, by his standards, was no excuse for not remembering that words could be made out much farther in methane than in air.

	He had had no experience with complex echoes under the surface, and it would be a long time before he knew about the speed/wavelength relation and such phenomena as diffraction, but Dondragmer went overboard anyway, and listened to the conversation for a moment. The downstream party was indeed on the way back. He joined in loudly.

	The group had made out and acknowledged his order to get the communicator. Then another pattern of hoots, as blurred and devoid of meaning as the first sounds in air along the rocks, interfered with the conversation.

	Words were indistinguishable. So were individual voice patterns. But the one other party under Dondragmer’s orders should be on land, and a quick flow to the Bree’s deck and back into the methane—Mesklinite hearing was not confined to any one part of the body surface—made it obvious that this noise too was originating in liquid. The same body of liquid which was flowing along the face of the rock fall.

	And into it. The sound must be coming from the captain’s group. At least one of them was alive.

	Barlennan could make out neither words nor individual voices either, but the leading fringe of the noise pattern, before the echoes ruined its structure, left him no doubt that it was a voice. He didn’t have to think. Words or no words, if he could hear the speakers, they should be able to hear him. If they heard him, they would know he was still alive. If they knew he was alive, they wouldn’t give up on him and his party. He and his men were as good as rescued.

	Except, of course, for minor factors such as how anyone could find them in this lightless maze where sounds came from all possible directions at once, that they had practically no food with them, and were in about the last place on Mesklin where anything edible could be expected to turn up unless it were washed in from outside.

	Come to think of it, why shouldn’t food wash in from outside? There were plenty of fish in the river, and the current was coming from that direction. Why were they lying here hungry instead of fishing? Well, they couldn’t see, of course, and you can’t hear fish—but it was something to think about. Hard. He ordered his men to think about it, and went back to the basic problem.

	Barlennan’s group knew, in a sense, where they were; the inertial tracker was readable. But there was no way to get its readings to anyone else; if the radio was blocked as it seemed to be, the tracker’s signals to Toorey must be equally unreadable to the Flyers. The echoes in the maze ruined any high-volume talking even if Dondragmer knew he was alive, and what else could lead rescuers close enough for quiet, echo-free talk? The captain could think of nothing. Could the mate, or the Flyers?

	Jeanette didn’t need to relay Dondragmer’s report to the other Flyers; enough people were already with her in the corn room. The relief that the captain might still be alive and sane—however garbled, the sound had been brief and seemingly better then raving—was tempered by the same doubts that Barlennan himself felt. Could that noise source be found? Could Mesklinites deliberately search, personally or otherwise, the maze under the rock fall? How long could the captain and his people live and remain sane to be rescued? On a more cold-blooded level, could the tracker be salvaged if he didn’t?

	The Drommian who voiced this question had the grace to show embarrassment, but even the human and other beings present couldn’t dismiss the thought completely from their minds. There were still Mesklinites at work salvaging the rocket contents, but there were no more trackers.

	Dondragmer thought of that aspect very fleetingly, and only to wonder about and dismiss at once the chance of using the tracker somehow to find its holders. It seemed far more practical to examine the area where the basket had disappeared. There might be meaningful clues among the rocks.

	He left a watch of four men on the Bree, and with everyone else not at the rocket set out upstream, carrying the radio. Some of the group had been sent that way earlier, and the rest did not catch up with them until reaching the point level with the eddy, days later. From this position they could see much farther up-stream, and the balloon bag which had been caught and separated from the basket was easily visible. The mate sent half a dozen sailors to salvage it, and with the rest took to the river, swimming across below the eddy and spreading along the foot of the tumbled fragments to look for other traces.

	There didn’t seem to be any. If the basket had brushed against anything on the way inside, either nothing had scraped off or, if it had, had vanished down river. The loudest possible hoot in air brought no response from the rocks, but when it was repeated from below the surface it was answered at once, more loudly than before. Several of the sailors muttered satisfaction; but all fell silent when they saw the mate looking thoughtfully into the widest of the gaps where methane was still flowing in.

	The eddy seemed as strong as the captain had reported. He had said nothing about the speed of flow into the rocks, but all could see that it was faster than anyone could be expected to paddle anything. It didn’t seem faster than a person could swim, but if one were too far inside to see daylight there would be no way of knowing which way to swim.

	"They’re in there somewhere," the mate said slowly. No one disagreed; no one said anything.

	"Kentherrer, use a safety line and check how deep it is here. Don’t go inside. Three of you, hold his line." He paused until Kentherrer was submerged. "Tell me if you have any trouble holding on," he added. He did not specify whether this meant to the rope or to the rock, and the sailors didn’t ask.

	The line was paid out for about four body lengths before it went slack. It was not pointing straight down; the swimmer had been carried a short distance into the cleft by the current, but seemed calm enough when he reappeared.

	"The bottom hasn’t any of that slush," he reported. "It seems to be sort of gravel. I suppose really fine stuff would be carried inside."

	"Could you get good footing on it?" Dondragmer asked.

	"Not—not very good, sir."

	The mate and the crew knew each other’s thoughts perfectly well. The former made some allowances for the objectivity of Kentherrer’s report.

	"We’d probably be safe enough, if we roped together. If anyone lost grip on the bottom, the others could hold him until he got it back. I don’t—see—anything to do but—go in and search."

	"Under all that?" one of the men asked before he could control himself. Dondragmer was silent for perhaps a minute. He was reasonably sure they would follow him if he went first, but wasn’t quite sure he could lead. Not there.

	"You may have something," he said at last. "Under it, in the dark, there’d be no way to tell where we were going or where we’d searched already. But over it—"

	By ordinary Mesklinite standards, over was little better than under. One could fall, of course, with a couple of hundred times Rim weight. But this was the Bree’s crew, who had been getting used to up and over in various ways for something like a hundred thousand days now. Over just wasn’t as bad.

	One of the sailors was sent back to the radio to tell the Flyers what the mate had in mind, and to relay any later messages. In a couple of days the mate and his remaining men were linked in a network of cordage, no one closer than eight body lengths to any other, and no one connected to others by less than four separate safety lines. The climbing was clearly not going to be easy or quick, but it would be as safe as the mate could arrange.

	Mesklinite legs are extremely short and their feet are not adapted for climbing, but they grip well on any reasonably rough surface. They have evolved for low as well as high gravity, and in the low-gravity latitudes there is always the risk of being blown away.

	These rocks were rough, in most places. The joints along which they had separated in the recent fall were not, for the most part, slickensides. Travel over them was fairly easy, except for the distraction of looking down so much of the time. Not even the sailors were totally immune to that fear.

	The rope spider web began to flow up and over the fallen slabs. Once all were away from the methane, Dondragmer ordered them to clamber horizontally upstream to the point where the eddy current went straightest into the maze. This served two purposes; it made it likely that they were upstream from wherever the captain might be, and could search downstream with reasonable certainty of passing him—whether they knew it or not. Also, it gave some practice in climbing before getting too far up.

	It even gave some practice in falling. Twice one of the sailors lost his grip and found himself hanging from a set of ropes. Both times a hoot of alarm was cut off sharply as the faller realized he was being supported, and managed to control his emotion with his intelligence. Most encouraging of all, neither time did anyone on the other end of the ropes lose his grip.

	So they started uphill. The rocks were noticeably cooler now. Even with the fog, there was little trouble keeping direction. Each time the web had moved about twice its own width the climbers paused and called loudly. After some days, they reached the top of the slope and were against vertical rock again; they moved a couple of web diameters downstream, and started down again.

	Every few days they called across the river to report their lack of result to the Flyers. They could make out the voice of the sailor on watch there clearly enough, but he had trouble untangling their words from the echoes. The messages, however, were simple enough—"Nothing yet" as a rule—and there was no real confusion.

	Back at the bottom, still fastened together, they swam back across to the radio, reported in more detail, then rested and went hunting and fishing. Fed as well, they returned to the up-and-down coverage of the fall.

	Every so often, an undermethane call was made; it was always answered by a sailor at the methane’s edge. Dondragmer wondered more and more seriously as the days went on what the lost group was doing for food. He was even slower than the captain in thinking of possible fish, but when he did, was much faster in realizing the problems of fishing in the dark. There had been very little food on the balloon, and it had been many days, now.

	It was the food question which decided Barlennan to take some action of his own. Fish either weren’t around or were able to sense groping chelae, and there had been no fishhooks aboard the balloon. He realized that any information the others might have about his location would be invalidated if they left it, but being found dead of starvation seemed a more serious risk. Besides, he could see no way of the crew having any such information. He had also realized that there should be no trouble in deciding which way to go, if they went; not only did the tracker provide a clue, but the current was still flowing past them, apparently unchanged. If they could travel against it, they should sooner or later reach the river.

	Unfortunately, while it was not flowing nearly as fast as any of them could swim, it was just in the wrong direction, and their own personal strength was failing—not seriously yet, because they’d been simply lying in the basket and occasionally answering what were presumably the mate’s calls, but swimming against a current...

	Even crawling against a current...

	Crawling would be better, if they could keep hold of the bottom. Better still, if they could anchor themselves to the bottom. The radio and the tracker would help with that, and should be brought along in any case. A few rocks would hold the basket down; but they couldn’t drag the whole basket against the current, whether it were ballasted or not.

	So they’d salvage material from the basket and, as well as they could in the dark, make a container to carry a few rocks. It might not work out; basket-weaving in the dark did not promise well; but it was better than starving passively.

	He told the others what they were going to do.

	A deafening roar, accompanied by a trembling of the rock on which the basket lay, suggested that he had the right idea.

	The same roar was heard by the others, even those at the rocket over a dozen miles away. The search web was headed downward on its fourth round trip. Each of its members felt the same quivering under his feet, and froze in position, looking wildly in every direction. The Flyers heard, but of course felt nothing.

	The sailor at the radio came closest to seeing; he could tell by the sound direction that the disturbance was somewhere upriver, even with the rumbling echoes that followed it, but there was still fog in that direction.

	No one, even Barlennan with the most restricted sight, had the least doubt that rocks were settling still. The Flyers wondered why; the Mesklinites, where. Neither could even guess at an answer, but the natives could, and did, hope. The operative fact was that if anyone could do anything whatever, it needed to be soon.

	There was no way that Dondragmer’s efforts could be speeded significantly; trying to climb around faster, it quickly became obvious, simply increased the time lost retrieving dangling climbers. The Flyers had already launched an observation craft to get better pictures and maps of the locale, but days would be needed to obtain those, probably more days to get any pattern for the continuing settling of the rock fall, and no obvious reason to believe that the information would really be useful to anyone but abstract researchers.

	But Barlennan could do something. Motion in the right direction, however slow, was better than staying where they were, and they did know the right direction. Up current.

	But they were already somewhat weakened by hunger. In a sense, they had some food; Karondrasee’s juice tank was perhaps half full. Unfortunately, the juice had been selected for its catalytic properties, as observed by the cook, on the plant tissue used for lifting fires, not for its caloric content. It was also most repulsive to taste—the cook knew that; he had distinguished his various trial samples by that sense, since he had no other laboratory facilities. Even the Flyers had admitted that there was little choice, though the alien chemists had expressed the very lowest opinions of that analytical technique.

	The tank, however, would be enough denser than methane to help hold them on the bottom, provided they replaced the air now partly filling it with liquid. There seemed at the moment nothing to be lost by diluting the juice and bringing the load along.

	Discussion was brief. All three of the crewmen could see the situation as clearly as their captain, and it was not just a matter of obeying orders.

	All four of them were now wearing the improvised hoods; even Barlennan had decided that it made things a little easier not to expect to see, and as long as the current flowed there was no real need to consult the tracker. There was no way of knowing just when the four of them submerged with radio, tracker, small basket of rocks, and juice tank with its top valve open, but it was long enough for one more roar of settling rock. Barlennan was actually delayed by this; he was slightly afraid that his men would be tempted into unwise haste, and insisted on a final recheck of every knot, both in the lines holding the equipment and those linking the travelers together. This delay did put a slight strain on discipline.

	Progress was slow. Even with the extra weight, traction was poor. The tank proved to be the least effective ballast and Karondrasee, who was carrying it, was frequently lifted from the bottom, and whenever this happened his next in line, Hars—cook and tank were last—had to find something to hold onto himself Sometimes there was nothing in reach, and they would lose in a few seconds several times as much distance as they had gained in the preceding few

	And they were getting hungrier, and more tired. None knew how much time passed. Every little while they would bellow to let others know they were still alive. They always heard answers, but there was no way of being sure whether these were coming more quickly or not. It would have been very encouraging if they had been.

	Travel did get easier after a dozen or more reports, but for a slightly discouraging reason.

	The current was losing its force. There was a perfectly plausible explanation: the space behind them, whatever it was, where the methane had been going was at last being filled up. Barlennan had been learning, however; he told himself firmly that there might be other explanations. He put the question before the others, more as a distraction than in hope of alternatives. He got none, but distractions were still useful even with the hoods; there was still a lot, no one could guess how much, of Mesklin overhead.

	It was also getting somewhat cooler, they could feel, though the slush underfoot was still slush and still provided very poor traction.

	And they were getting hungrier a the time. That in itself made travel more and more difficult. Chemically, evolution in an energy-demanding environment had given them the equivalent of a very large human glycogen reservoir for their size, but even that had its limits. They were nearing those limits.

	The juice tank was now very dilute; they had not bothered to close the valve. This made the taste more bearable when they finally gave up and tried it. However, there is little to be gained by adding more catalyst, even just the right catalyst which this was not, when the supply of reactant is nearly gone. No one felt any less hungry than before, and the cook/flight engineer, whose digestive equipment might have been affected by his earlier experiments, was extremely uncomfortable for a time. He was quite unable to crawl or swim, and the party had to wait where it was.

	Another roar and shudder of settling rocks enabled him to find some strength, and they moved on. The current was nearly gone, and they were guided now by the tracker, much more slowly even than before. The cap-rain made the next report hoot by himself, hoping that its relative weakness would give the listeners a suggestion of their plight.

	It didn’t work; the sailor on watch below the surface who had been doing the answering didn’t notice the difference. There was a good reason for this, it was realized later. The captain was now much closer to the searchers. However, the rumbling echoes of his voice still lasted about as long as ever and hid the volume difference. He himself failed to notice any change in the answer; he blamed it later on the distraction caused by hunger.

	Hats, more than any of the others, hated to feel his energy going. He also hated to fail, and he still felt responsible for the tracker he was carrying. He probably had the least idea of any of the four why the echo problem should be less in air than in methane, but he had reached a point where anything seemed worth trying.

	They had done all their calling under methane, for obvious reasons; sound traveled better there, as everyone knew. On the other hand, one grew tired more quickly there, though Hats didn’t know why. One was lighter below the surface, obviously, but for some reason had more endurance above. "Hydrogen concentration" was not even words to him. But if there were anything to climb out on, he knew he would feel better.

	He began to mutter aloud. Just mutter. He would have done something else if he had been leading, but the captain was in front. The others could hear, of course, and Barlennan began to worry. Sherrer’s lack of balance had been serious enough; Hats was by far the most powerful of the group, even now If he were to panic, it might make the final difference. Especially with them roped together. After a little thought, he spoke to the sailor.

	"Hars, what’s the matter?"

	The pilot was actually embarrassed. "Well, Captain, I was wondering whether we could find a slope and get up in air for a little while. We could do with some rest, and it would be better than under methane. I didn’t realize I was thinking out loud."

	Barlennan thought quickly. Shortage of air—hydrogen—at this point was not actually as serious as shortage of food, but it was certainly much more uncomfortable. It didn’t much matter where they were if one of the rock settlings took place near them. They were as likely to be found in one place as another, after all; and if they really couldn’t get out from under— "All right. Change the setup. Hars and I will travel side by side, a rope length apart. Sherrer will be at my right, Karondrasee at Hars’ left. It will be harder to keep the line straight, but we’ll be more likely to find an upslope."

	It took some time to rearrange the safety lines, but they were slightly rested when it was done and they were advancing in the new formation. It was harder to travel, however, since they could not be as much help to each other. Even the captain was ready to call a halt where they were when the rope connecting Karondrasee and Hars dragged on the bottom.

	There was some sort of bulge. Hope of a sort began to rise as they examined and found a continuing slope. A solid one, of rock. The hope was mostly for comfort, not rescue, but the comfort was that of fresh air. They crowded together and began to creep upward. The slope was very shallow, and not difficult to climb even in their conditions; and for a while all feared that it might not reach the surface.

	Fortunately. All but Hars had to stop for rest before they reached surface. With the four huddled together to rest, there was enough slack to let the pilot crawl a little ahead of the others, and in less than five body lengths he broke the surface.

	With his encouragement and help, the other three also emerged into air, and relaxed gratefully.

	Nearly starved, they were really in no state for rest to do them much good, but they could still enjoy the sensation. Even Barlennan waited much longer than he should have before issuing the order to go on. His mind and conscience argued against giving up, but he knew that more time in air would not really help. Another rock shudder emphasized this, but still he hesitated. Lying still felt so good— So he had not yet spoken, and not yet decided to, when airborne sounds reached them.

	Voices. Not really understandable yet, but obviously broken up into words this time. The four hooted in unison, reflexively. Shorter wave lengths don’t diffract so badly, and sound waves are much shorter in air.

	The only real question then was whether Dondragmer’s people would climb down or Barlennan’s climb up, and that was easy to settle.

	The distance wasn’t great; the mate’s party could see how close they were to river level, but the captain’s group lacked the needed strength. The members of the net above were out in daylight, able to look down at the spaces below, where they would descend into unknowable depths. Well, not really unknowable; the captain and the others obviously weren’t very far down, but the word was down. But they could climb down.

	The mate, still attached to four safety lines, descended with food, and after half a dozen false turns managed to deliver it. Then, one at a time, rested and fed, each with three lines firmly attached to him, the balloonists were partly hauled and partly climbed up to the web. A sailor brought the lines back down for the next rescue, and another one for the next, and when one descended for the last time, he and Barlennan used two ropes apiece to get back to daylight.

	There had been some debate about the communicator and the tracker.

	The former had been hauled up ahead of the captain on a pair of carefully fastened lines, but the inertial equipment had gone up even earlier, still fastened to Hars. It remained attached to him until everyone had crossed the river to the other communicator; he refused to abandon the duty until the whole group, except the ones still at the rocket, was together.

	The Flyers understood, they thought. They certainly didn’t complain. All Barlennan could overhear and understand was another of their theoretical arguments.

	"Look, there’s only one explanation. We know that rock is sedimentary— "Know?"

	"Well, it’s pretty obvious. One of the layers of the plateau, just below the foot of the cliff, has to be ammonia. That’s mineral there. A lot of it was melted by the falling rock, and the Mesklinites smelled it—"

	"Smelled something like it.

	"What else could that be?"

	"How do I know? I’m not a Mesklinite."

	A third voice cut in. "The two of you are just gabbling. We haven’t seen a layer that looked like ammonia—it’d be white, like ice."

	"It would be ice.

	"All right, but we haven’t seen any."

	"It’s underground at river level."

	"But how could—?"

	"That’s what I’m saying! We’ve got to check—I mean, Barlennan’s people have to check—"

	"How? They don’t have drills, or shovels, or picks, and you can’t expect a Mesklinite to go tunneling, do you?"

	The captain had never heard this verb, but context suggested its meaning, rather too clearly.

	"Why not? Barlennan’s had lots of time underground now, and he’s still all right."

	"How do you know he is?"

	The captain started to tune out, as usual. Just another of the theory-based wrangles among Flyers, which of course might lead to something later.

	Then he saw what the something probably would be. The Flyers were very persuasive beings— Any being with muscles and a nervous system complex enough to consider alternatives consciously can shudder. Dondragmer was obviously listening, too.