He chased the cougar, and kept it in sight, until it went over the second rim wall.
Here he dropped over a precipice twenty feet high, to alight on a fan-shaped slide which spread toward the bottom.

It began to slip and move by jerks, and then started off steadily, with an increasing roar.
He rode an avalanche for one thousand feet.

The jar loosened bowlders from the walls.

When the slide stopped, Wallace extricated his feet and began to dodge the bowlders.

He had only time to jump over the large ones or dart to one side out of their way.