Here, evidently, was where the animal had crossed.

It must have been a very small animal, Tom thought, to have sought an easy place for crossing.
Having thus determined the exact place of crossing, Tom concentrated his attention on this spot, examining the bark systematically, inch by inch.
But no vestige of a clew rewarded his microscopic scrutiny.

He was baffled and his curiosity and determination rose in proportion to the difficulties.

His big mouth was set tight, a menacing frown clouded his countenance, so that instinctively little Skinny refrained from speaking to him.
Tracing the apparent line of the animal's crossing over the log, Tom scrutinized the prints on the other side, that is, the side nearest camp.

Here the prints were very clear by reason of the crust of mud caused by the dampness usually found near logs and fallen trees.