Topography of the St. Ellas Range. 191 



sembles the tyjoe of mountain structure characteristic of the great 

 basin. The dip of the tilted blocks is northward. 



The crest of the St. Elias range, as already stated, is composed 

 of schists which rest on sandstone, supposed to belong to the 

 Yakutat system. The geological age of the uplift is, therefore, 

 very recent. The secondary topographic forms on the crest of 

 the range have resulted from the weathering of the upturned 

 edges of orographic blocks in which the bedding planes are 

 crossed by joints. The resulting forms are mainly jDyramids and 

 roof-like ridges with triangular gables. Extreme ruggedness and 

 angularity characterize the range throughout. There are no 

 rounded domes or smoothed and polished surfaces to suggest 

 that the higher summits have ever been subjected to general 

 glacial action ; neither is there any evidence of marked rock de- 

 cay. Disintegration of all the higher peaks and crests is rapid, 

 owing principally to great changes of temperature and the freez- 

 ing of water in the interstices of the rock ; but the debris result- 

 ing from this action is rapidly carried away by avalanches and 

 glaciers, so that the crests as well as the subordinate features in 

 the sculpture of the cliffs and pyramids are all angular. The 

 subdued and rounded contour, due to the accumulation of the 

 products of disintegration and decay, the indications of the ad- 

 vancing age of mountains, are nowhere to be seen. The St. Elias 

 range is young ; probably the very youngest of the important 

 mountain ranges on this continent. No evidences of erosion 

 previous to the formation of the ice-sheets that now clothe it have 

 been observed. Glaciers apparently took immediate possession 

 of the lines of depression as the mountain range grew in height, 

 and furnish a living example from which to determine the, part 

 that ice streams play in mountain sculpture. 



