322 



BOTANICAL GAZETTE 



[may 



m 



In due time the climate began to change and the amount of snow to 



became bare during the summers. 





decrease accordingly. Finallyj the winter snowfall" decreased to 

 such an extent that the summit of the divide and the gentler slopes 



These surfaces had heretofore 



been protected by their 

 load of snow from the 

 process of weathering. 

 Now, however, began the 

 work of frost and of tem- 

 perature changes, which 

 is responsible for the 

 condition of the summit 

 today. The thinness of 

 the covering of rock frag- 

 ments on these surfaces 

 is due to the protection- 

 from sudden changes of 

 temperature afforded the 

 solid rock beneath by the 



broken 



with 



i3K^*f' 



the layer of vegetation 

 that has become estab- 

 lished upon it. 



In the meantime the 

 daciers themselves stead- 

 ily shrank, because of the 

 decreasing supply of snow 



at their sources 



The 



Fig. 3.— View in Glacier Gorge, showing glacial 



large 



accumulation of 



J- -*^.- i*. vjia^iui ^juigc, biiuwiiig giaciai ^ ^ n ^ 



topography and wet meadow areas on ledges; a neve in the cirqUCS, llOW- 

 glacial lake in the foreground, and snow banks below 



the cliff, 



s. 



ever, enabled them to 

 hold out long after the 



perennial snow mantle of the summit and exposed slopes had disap- 

 peared. In fact, there still remain at the heads of several of the 

 canons remnants of the former ice tongues, which, though small, are 



true glaciers. 



The canons thus formed exhibit the usual glacial characteristics 



