No matter though it may be several hundred feet in height he holds straight on, as if about to dash headlong into the throng of booming rockets, then darts abruptly upward, and, after alighting at the top of the precipice to rest a moment, proceeds to feed and sing.

His flight is solid and impetuous, without any intermission of wing-beats,--one homogeneous buzz like that of a laden bee on its way home.

And while thus buzzing freely from fall to fall, he is frequently heard giving utterance to a long outdrawn train of unmodulated notes, in no way connected with his song, but corresponding closely with his flight in sustained vigor.
Were the flights of all the ouzels in the Sierra traced on a chart, they would indicate the direction of the flow of the entire system of ancient glaciers, from about the period of the breaking up of the ice-sheet until near the close of the glacial winter; because the streams which the ouzels so rigidly follow are, with the unimportant exceptions of a few side tributaries, all flowing in channels eroded for them out of the solid flank of the range by the vanished glaciers,--the streams tracing the ancient glaciers, the ouzels tracing the streams.

Nor do we find so complete compliance to glacial conditions in the life of any other mountain bird, or animal of any kind.

Bears frequently accept the pathways laid down by glaciers as the easiest to travel; but they often leave them and cross over from canon to canon.