These afforded good footholds, but the surface curved more and more steeply at the head, and the pits became shallower and less abundant, until I found myself in danger of being shed off like avalanching snow.

这些提供了良好的立足点，但表面在头部弯曲得越来越陡，坑变得越来越浅，越来越少，直到我发现自己有像雪崩一样被甩掉的危险。