They slid on their haunches.

Fortunately the slope grew less steep, and Slone could see below where it reached out to comparatively level ground.

Still, a mishap might yet occur.

Slone kept as close to Nagger as possible, helping him whenever he could do it.
The mustang slipped, rolled over, and then slipped past Slone, went down the slope to bring up in a cedar.

Slone worked down to him and extricated him.