So he pushed himself gradually close up to a ledge, which, while of indifferent height, still protected his body somewhat.

On this ledge he expected to notice scratches which indicated that the trail passed over it.
It was as he suspected,--the rock was slightly worn by human feet; but of fresh tracks there could of course be no trace here, for only long and constant wear and tear, and not an occasional hurried tread, can leave marks behind.

But Topanashka noticed a few fragments of rock and little bits of stone that lay alongside the old worn-out channel.
Without lifting his head, he extended his arm, grasped some of the fragments, and began to examine them.
Loose rocks or stones that have been lying on the ground undisturbed for some time, always have their lower surface moist, while the upper dries rapidly.

When the yellowish tufa of these regions becomes wet, it changes colour and grows of a darker hue.

Topanashka had noticed that some among the stones which he was examining were darker than the others.