They subsequently learned, as a solution of the mystery, that at that time the small-pox was making dreadful ravages.

Thousands were dying and it was feared the whole tribe would perish.

The Indians in their terror, had secluded themselves in the remotest solitudes.
Winter was now approaching, with its freezing gales, its drifting snows, its icy streams.

It was necessary to find winter quarters for two or three months.

The region, drained by the Yellowstone and its tributaries, extends over thousands of square miles.