"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 ship building 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 traveled 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 river bank. 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 gray 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 s.p.a.ce 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 carrying 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 traveling 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 s.p.a.ce 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 a.s.sured 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 pa.s.sed 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 pa.s.sed 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 that 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 a.s.sent 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 worth while. 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 expected 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 alt.i.tude 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 were 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 were 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 p.r.o.nounced 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."