igoS] ■ 



COOPER— ALPINE VEGETATION IN COLORADO 



321 



with it, being covered with a thin layer of frost-broken fragments. 

 Some of the ridges bear high rugged peaks, but in most cases they 

 decrease gradually in altitude away from the divide, and frequently end 

 in long interlobate or medial moraines, where the adjacent glacier 

 tongues met or coalesced. The floors of the canons descend toward 

 the lower altitudes in an alternating series of very gentle slopes and 

 abrupt steps, the latter often 30™ or more in height. 



B. Historical. — A glance at the physiographic history of the 

 region will make clearer the present conditions and processes. For 



^K|*^ 



^ ^/-P^ 



.tJ 



. ■ ^^ 



^ 



V 



■■^i^4S^-^' 



Fig. 



2. 



Summit of the divide near Mt. Tyndall; a more detailed \iew of the dry 

 meadoAv, showing also the top of chffs that surround a glacial cirque. 



tlie purpose of this paper, it is unnecessary" to go back farther than 

 the time of Pleistocene glaciation, since during that period practically 

 every trace of vegetation must have been destroyed. The Front 

 Range in the region studied was glaciated during the Pleistocene 

 period over a width of about 25'^™^ The summit of the range was 

 deeply covered with snow, which, accumulating in larger quantities 

 in favorable locations along the flanks of the range, became consoHr 

 dated at these points into glacier ics and commenced the work of shap- 

 ing and modifying the canons. 



' King, Clarence, Exploration of the Fortieth Parallel. 



