Two broke away and ran with the led horses.

It was a rough place, littered with large rocks and fallen trees.

In their panic the horses floundered over those, but a little farther down came on a bare, shelving ledge that overhung the brook.

Probably they could not see where they were going, or else those behind shoved the foremost off the brink; at any rate, six of the horses went headlong down into the rocky bed of the torrent, whence instantly arose heart-rending squeals of pain.
It had all happened so suddenly that we could not possibly have prevented it.

In fact, we had no more than picked ourselves up from among the snowy logs and stones when they were down in the brook.