remaining, for their own reasons. However, the question of just what was likely to be found gave rise to much rather barbed comment on Sulewayo's part. "I don't see how you can expect to find any trace of civilized work here," he said flatly at one point. "The animal and plant life of this planet is at a stage of evolution corresponding to something like Earth's Pennsylvanian age, when the amphibians were the highest known forms of life. I'm not saying that there couldn't be such a thing as an intelligent amphibian. But I do say that the normal set of evolutionary forces which, on both Earth and Viridis, produced creatures of the amphibian pattern could have done that or produced an intelligent fish; not both. If the latter ever evolved, it failed; for the amphibians—pardon me, amphibids—are here. To get an intelligent amphibid on this world will—or would, if the sun were to last long enough—require another orogenic period with the accompanying climatic changes. Then you'd stand a considerably higher chance of getting reptiles instead, if the comparative work done on over four hundred planets carries any meaning."

"I don't doubt the value of the work at all. You are very probably correct. It did not occur to me to expect remains of intelligent amphibians. I saw no reason to pre-suppose that anything in the way of artifacts which I might find would necessarily be native to this planet."

"You think there were other visitors from outside the Beta Librae system?"

"The possibility certainly exists. Here we are."

"But for Pete's sake! Do you really expect that they stayed long enough to build a city, or do you think you have the remains of a camp like ours, or what?"

"I don't think anything. It has been suggested that such people did come, and stayed long enough to—"

"And you think you've found them."

"I think nothing, except that I have found, with Rob's help, something which neither his professional knowledge, nor mine, nor even yours, is able to explain; and I think an explanation is desirable. I hope you won't consider me discourteous for pointing out that each time you have tried to accuse me of jumping to conclusions, you have been able to do so only by jumping to some yourself. I might further add that the suggestion that this planet had been stocked with its present supply of life types by visitors from space was advanced by a paleontologist, not by one of my colleagues. I gather he could not 

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