the wind also was crammed in narrowly , and whistled a little where it passed over sharp edges or crevasses in the rock ; a loose slope challenged them awhile in climbing , and laurence slipped badly on the other side , sliding with a tumble of loose pebbles , sand creeping into all his clothing ; falling backwards he caught himself awkwardly on his hands , which sank wrist-deep into the gravel as he slid a little further .