the men were awake well before sunrise. the human body takes a long, long time to accustom its physiological cycle to a change in something as fundamental as the length of day. but they did not attempt to resume flight until the green star was once more in the sky. mitsuitei put forth a tentative suggestion that the interval be spent in a visit to the "city" site he had seen the night before, but mclaughlin vetoed it.

"going on foot through the jungle at night is a fool's game, though i admit people sometimes get away with it. i could get you there, but even if we turned around and came back immediately there'd be a lot of time wasted. dr. lampert went over all that last night. look, that hill of yours is right by the river. after we're set up in the main camp, it will be relatively easy to drop down to it. we have collapsible boats. unless we camp above the rapids, you won't even have to fly. even if we're farther upstream and do have to use the 'copter, the trip will take only a few minutes."

mitsuitei had agreed, though with evident reluctance. no one else had any desire to go out; there was not enough rock exposed on the hilltop to excite the paleontologists, the hill itself presented nothing unusual to lampert's geophysical eye, and mclaughlin was in no hurry to get to work. they waited, therefore, until the "claw"—lampert had recalled beta librae's arabic name—had risen and the skyglow been replaced by its emerald brilliance; then the journey was resumed.

it took, as mclaughlin had said the night before, only a few minutes. the hill where they had slept was less than five miles from the face of the mountain range. only the haze of the night before had prevented their seeing it. the river emerged from a canyon some fifteen hundred feet in depth, a couple of miles to the south of their eastward course line.

lampert, in hopes that the usual haze might not be too evident at this hour, climbed above the level of the cliff top to get an idea of the mountain range as a whole; but he was disappointed. for nearly an hour he cruised over the area, now several thousand feet above the western cliffs and then well below them. it slowly became evident that the range represented a single block, which had been tilted upward on the west side. the opposite slopes were very gentle, merging so gradually into the general peneplain level of the continent that it was impossible to say decisively just where the range ended. the river did originate somewhere beyond the range, cutting entirely through it, and as the guide had said, its current was not particularly swift. lampert had much explaining to do. after all, water should have drained toward the low side of the block.

"it seems evident," he summed up his ideas as they hovered once more over the western cliffs, "that the river was here before this particular bit of block tilting occurred. this planet does have some diastrophic forces left in its crust, in spite of its generally smooth nature. apparently this just represents the end of a long period of rest, such as the earth has had several times. as a matter of fact, i have no business calling it the end of such a period; it might be fifty million years before the world will be generally mountainous again."

"why do you say again, rob?" asked krendall. "according to findings of your own colleagues, this planet has hardly been solid for forty million years. could it be this flat now if it had ever been markedly mountainous in that time?"

"good point. i don't know, but would be inclined to doubt it. well, we'll cancel the 'again' if it will make you happy. in any case the block forming this range came up slowly enough so that even this river, with its relatively low cutting power, was able to keep pace with it and not be deflected. probably—" he glanced at mitsuitei—"the rock of which it is made will turn out to be quite strongly jointed. it looks rather that way from above—the river course, i mean. a lot of right angle, or what were once right angle, bends."

"we'd better go down and look for a camp along the river somewhere," put in mitsuitei. "let's start at the cliff end. then we may wind up reasonably close to that hill—and i still want to look it over, joints or no joints."

"fair enough." lampert eased the helicopter once more downward until they were only a few hundred feet above the jungle, moved along the cliff face until they reached the canyon, and, very cautiously, entered. his caution proved unnecessary. the air currents in no way resembled the treacherous hodge-podge he had expected, at least not over the center of the river. a steady wind was blowing into the canyon mouth, but did not seem to be eddying very much even at the numerous bends.

to the archeologist's annoyance, two sets of rapids were passed before a place was reached where the bank was wide enough for a camp site. at this point a fairly large side canyon entered the main one from the north. where its central stream joined the main river a gravelly area several acres in extent offered itself for the purposes of the scientists. lampert brought the helicopter down on this surface. the surroundings looked promising; the cliffs facing both canyons looked reasonably accessible on foot for some distance, at least along their bases. climbing appeared to be impracticable for the most part, as the rock walls rose sheer except for the occasional joints which lampert had predicted; but the material was certainly sedimentary, and everyone but the guide tumbled out of the flyer with a glow in his eyes which promised a speedy scattering of the party.

with some difficulty, mclaughlin got them together. a site, some twenty yards square, was selected against one of the cliffs and fenced off. the big, prefabricated sheet-metal "tent" was erected and its tiny conditioning unit installed; sleeping and cooking gear were placed inside. that completed, geologist's hammers appeared as though by magic; and mclaughlin realized that he had better do some explaining before he lost a scientist or two. once more he called them together.

"all right, gentlemen. i admit the necessary camp work has been done, and there should be nothing to keep you from your projects. still, there are some things you had better understand.

"having canyon walls on all sides does not make this place safe. every carnivore and poison lizard on this planet could get to us by way of the river—even the ones which look like land animals. every one of them could swim under water from a point out of sight in either direction to where you are standing; and if you think he would have to come up at least once to judge your position, guess again. i don't know how they do it, and neither does anyone else; but a felodon could submerge around the bend up there, come up behind the helicopter out of sight of any one of us and be waiting when we marched around the machine. therefore, go armed at all times. i know you want to cover a lot of ground, and can't stick in one party; but i insist that you do not go anywhere alone. take at least one companion. preferably one who is not a member of your own field. if you two paleontologists are together, for example, it seems more than likely that you'll be found with your heads in the same hole in the rock. when one of you has to dig, make sure the other has his neck on a swivel. i know this will slow your work, but not as much as if the work had to wait for a new investigating team from emeraude—or from earth.

"you've seen most of the dangerous animals in the zoo at emeraude, so i won't waste time describing them. just remember that you won't always hear them coming. you'll have to use your eyes.

"all right, dr. lampert. you're the boss, as far as the scientific work goes. who does what, and where?"

the geophysicist gave no sign of having detected the humor in the guide's remark, but began speaking at once.

"i should say that the main canyon upstream and the side one in the same direction should be covered first. we've already used up a good deal of today, and would waste more breaking out the boats. ndomi and i will go up the main stream; hans and take can take the other. don't hurry. if anything looks good, take the time to investigate it on the spot. of course, if it is obviously a major job, just mark it and go on. there's no sense in one man's trying to exhume a six-foot lizard skull.

"since this region must have been sea when the limestone was deposited, there's not much chance of land animals. however, we want as complete a chronological series as possible, so do the best you can on this level. we'll try for higher formations later. there should be plenty farther upriver, if this block is tilted the way it seems to be.

"string, perhaps you'd better go with take and hans. set out when you're ready. be back in—" he glanced automatically at the narrow strip of purplish-blue sky, then at his watch—"four hours; then we'll compare notes. after that we can either concentrate on one place or the other, or break out the boats and cross the streams, as indicated."

twenty minutes later the parties were out of sight of each other and the helicopter. lampert had spent the first few minutes of the walk wondering whether he had been too obvious in arranging for both the guide and krendall to accompany the little archaeologist; but he quickly convinced himself that mclaughlin's speech had covered the arrangements pretty well.

in any case, he would probably have been distracted soon enough. the cliffs were interesting. limestone, evidently, as expected—but rather dense, at that; maybe some barium replacing the calcium? or was the gravity different enough to destroy his judgement for such a small fragment? probably not. he was actually using inertia more than weight in making his estimate. anyway, the stuff was certainly a carbonate. it frothed satisfyingly under a drop of acid from lampert's kit.

and there were fossils. sulewayo's form was bent over a spot on the cliff face, examining minutely; but lampert could see others from where he stood. none seemed remarkable. most were rather evidently shellfish. he carefully refrained from giving them names according to the genera they resembled in earth's rocks; sulewayo and his colleagues frowned on the practice, which could be most misleading. he could not, however, resist the temptation to think of them as scallops.

"what do you have there, ndomi?" he knew the other would not have spent so long on any shellfish.

"not sure, precisely. maybe vertebrate, maybe not. what could be armor and what could be ribs all mixed up. i think i'll mark it for future reference."

"i suppose it'll be another devonian whatsit, like everything else on this planet, when you do decide."

"pennsylvanian would better describe the world as a whole. barring that, you may be right. rob, if you'd give me a hand here we could get some basic work done."

"eh?"

"you say this is a tilted block. in lowest formations right now. i'd like to get photos and if possible specimens of as many different varieties of shellfish as possible, at each level. then it may be possible to set up some sort of temporal sequence—and use the things as index fossils if animals do evolve on this be-nighted mudball. if you could get me some radioactive dates at two or three nicely scattered levels, it would also help."

"thanks," returned lampert drily. "i could use material like that myself. i can tell you what you probably already know—you're not likely to get anything of the sort from limestone."

"well—intrusions are always possible."

"you watch for 'em, then." the pair went to work.

two hours out, a little more than one back. there was no one at the helicopter when they reached it, but the other group came in only a few minutes over the four-hour limit which lampert had imposed. a comparison of notes over the meal which had been quickly prepared indicated that the second group had gone farther in point of miles covered, but had accomplished less work. krendall had had the same idea as sulewayo. but he had not attempted to carry it out since his canyon did not cut across the range, and would presumably not furnish a continuous change in formations.

lampert and sulewayo, as it happened, had not found any evidence of change themselves. the last fossils they had found were at least superficially identical with the first. there was the usual evidence of bedding, and it had been quite evident geometrically that the walk had taken them to originally higher, and presumably later, levels; but in what must have been eight hundred feet or more of original deposit, there seemed to have been no significant change in the fossil life. what eight hundred feet would mean in point of time, of course, no one had the least idea. there was not even a good guess as to how fast carbonates might be expected to precipitate in a viridian ocean. anyone could compute the carbonate ion equilibrium between atmosphere and sea, but no one knew anything to speak of about carbonate-precipitating organisms of the planet.

mitsuitei changed the subject slightly at this point.

"we found several of the joints you predicted," he said to lampert.

"oh? very wide? we didn't spot anything that was obviously a joint. but there were several small side canyons—all narrow enough for us to wade or jump their central streams—which might have started life that way."

"ours were quite narrow, and bore traces of volcanic ash at the bottoms."

"eh?"

"that's right, rob. here's a bit of it i brought back. i thought you might want a little corroboration on that one." krendall handed over a bit of crumbly tuff as he spoke. lampert examined it with pursed lips.

"maybe we'd better get back into the air, and search the neighborhood for volcanoes," he said at last. "i can't bring myself to believe in two full mountain-building cycles on this planet—and if i could, i'd have a hard time swallowing the idea of these limestone layers coming up, going down, and coming up again unaltered. how deep were these volcanic deposits?"

"variable. shallowest in the wider joints; in the very narrow ones, up out of sight."

"suggesting that they've been washing out for some time since the original settling. anything organic in them?"

"nothing turned up yet."

"do they extend below the present river level, or what?"

"they're at least down to it. we couldn't do any major excavating."

"if they run much below," muttered lampert, "i'll join the roster of geophysicists who have been driven off the rails by this woozy world. well, let's assume as a working hypothesis that the volcanic activity is relatively recent. that will at least have the advantage of keeping me sane, until something comes up to disprove it." he finished his meal in silence, while mclaughlin gave a reproving lecture on the matter of wading.

there was still a little daylight to go when all the men had eaten; and lampert, sulewayo and the archaeologist took the helicopter up the main canyon to check on the possibility of walking to any really new deposits.

they were sure, from changes of color already seen at various levels up the cliff face, that these existed. but it appeared that the lowest of them did not reach river level for more than a dozen miles. the distance was less mapwise, but the canyon, winding back and forth around what the geophysicist still felt must be joint-bounded blocks, went a good two miles in other directions for each one that it led eastward. realizing this, the explorers lifted the helicopter and began checking as close to the cliffs as lampert dared at higher levels. in this way they worked back toward the camp site. once again it was mitsuitei who first spotted something of major interest.

"found another city, take?" asked sulewayo at the other's call.

"not exactly. it's—well, i guess it's really a system of those joints you keep talking about. still, it looks awfully regular." he sounded a little wistful.

"it does." the paleontologist nodded slowly. "as you say, it's probably a joint system. also, it's probably full of volcanic ash, if my eyes don't deceive me. rob, what's the chance of a landing on one of the shelves? there are at least three formations accessible on foot from that point; and i could get some more tuff samples to make or break your peace of mind, while i was doing my own work."

lampert examined the area carefully. like earth's grand canyon, this one receded from time to time in shelves where softer layers of rock had worn further back, or the orogenic processes had paused to give the river a longer bite at that level. the cracks mitsuitei had seen formed a neat crisscross pattern on the top of one of the shelves. some of them betrayed their nature by emerging from its vertical face. it was admittedly an unusually small-scale joint pattern, at least for this mountain system, and might well contain readable evidence of the forces which had shaped the area.

however, they had only one helicopter. lampert slowly shook his head in negation.

"i'm afraid not, ndomi. your shelves may be big enough, but they're not level enough. i'd have to make a swinging landing, and i'm not that good a pilot."

"well, how about letting me down on the ladder? we have a hundred feet of that, so you could be up above the next shelf while i went down. you'd have plenty of blade clearance. that next level goes back a couple of hundred feet."

"that might be all right." lampert spoke hesitantly. "you certainly have the right to risk your own neck on the climb if you want to. we won't try it tonight, though. i'd like to check with string on the advisability of your being there alone. the place looks pretty hard to reach for anything that doesn't fly, and i don't know of any really dangerous flying things on this world; but we'd still better check."

"all right with me. i'd just as soon have a full day, anyway."

"if ndomi will be spending a day alone up here, how about having string take me to the other place, and settle that point once and for all?" asked mitsuitei as the helicopter eased downward toward the camp. "that would still leave hans and you to form another team for whatever else you want to do."

"that should be all right. it'll depend, though, on whether string thinks it's safe for a man to work alone on that shelf."

the proposition was put to mclaughlin as soon as the machine was landed. to lampert's surprise, the guide gave a qualified approval.

"remember," he concluded, "i don't know what lives on the cliffs. it's country i've never covered. all i'm saying is that no viridian animal i know of could get there, except flying ones; and they're nothing to worry about, especially in the day-time. i'd like to go with you to look over the place when you take him up tomorrow, and strongly recommend that he carry a communicator as well as a weapon; but unless i see something you haven't mentioned when i do go, i would say it was all right...."

once more the felodon reached the river, but this time it did not cross. it was no longer heading straight for the helicopter. hills had not altered its course, but the cliffs had. they formed a wall on its right which was too nearly vertical for its agility and strength. even this barrier, however, had caused no visible hesitation or doubt. it had swerved, followed the base of the wall to the point where the river emerged and plunged in as promptly as it had done before. few amphibians have ever lost the art of swimming when their larval gills vanished; the feeble current meant nothing to the felodon.

it turned upstream and went on its way.