behind him the terrace ended in another straight drop of several hundred feet. A quarter of a mile on either side, the flat surface ended; to the west, by narrowing until the two walls became one; at the other end, it was cut off as far as he was concerned by a joint penetrating apparently the full depth of the canyon.

There were several other cracks in the wall facing him. Like those in the tributary canyon explored by Krendall and Mitsuitei, these were packed with volcanic detritus. This was hard to reconcile with the suggestion that erosion had been long at work. In such a case, the higher portions should have washed away long before the material found at the canyon bottom.

Examination at close range suggested a possible explanation. The tuff at this point was fairly well cemented. It seemed reasonable to suppose that the joints had been present before the mountains had started to rise; that a volcanic mud flow had filled them with detritus; that the new material had then been cemented by dissolved material coming from above. This would make the top levels of the tuff more resistant than those lower down, where the cementing minerals had not reached, and account for what had been seen so far.

The hypothesis also implied a plentiful supply of fossils. Volcanic mud flowing into a crack in the ground should carry plenty with it. Sulewayo set to work with a hammer, and was presently soaking with perspiration.

He was tempted to remove some of his clothing; but this had been treated chemically to repel Viridian insects and caution prevailed. McLaughlin had not mentioned any dangerous biters or stingers, and in all probability his blood would not be to the taste of any such creatures on this world—but if the mosquito or tick did not learn that fact until after it had tried, Sulewayo would hardly profit by it. In any case the temptation to strip passed quickly. In only a few minutes, his attention was fully occupied by his work; for the expected fossils proved to be present in very satisfactory numbers.

Most seemed rather fragmentary. Apparently the original creatures had been tumbled about rather badly before the medium hardened. However, the remains were definitely bones, as he had expected and hoped. For some time Sulewayo was occupied alternately digging out more fragments and trying to fit the more hopeful-looking specimens together, although he had no success at the latter job. Then evidence of a more complete set of remains appeared, and he instantly slowed down to the incredibly meticulous procedure which 

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