There was no alternative.

He saw none, would admit none.

He found time, as he went past her, to grin at her, and the grin, though a trifle wan, contained much of its old mockery and contempt of her judgment of him.
The black raced on for a hundred yards, and what ensued might have been an accident, or it might have been the deliberate result of the black's latest trick.

He came to a sudden stop, rose on his hind legs and threw himself backward, toppling, rigid, upon his back to the ground.
As he rose for the fall Calumet slipped out of the saddle and leaped sideways to escape being crushed.

He succeeded in this effort, but as he leaped the spur on his right heel caught in the hollow of the black's hip near the flank, the foot refused to come free, it caught, jammed, and Calumet fell heavily beside the horse, luckily a little to one side, so that the black lay prone beside him.
Betty's scream was sharp and shrill.