MOUNT RAINIER 



recent times. Out of this plateau, formed by the up- 

 lifting of the plain, has arisen through the active attack 

 of erosive forces the truly mountainous character of 

 the district. Erosion has been at the maximum in the 

 mountains because of the heavy precipitation. Pre- 

 cipitation in the high mountains being chiefly in the 

 form of snow has led to the formation of glaciers, 

 producing thereby a rapidity of erosion of the first 

 order. The active work of ice and running water has 

 given to the mountains an extremely rugged appear- 

 ance, characterized by valleys of great depth extending 

 into the very heart of the mountains and with precipi- 

 tous divides. 



It must be understood that the time consumed in 

 the uplifting of the Cascades, and the conversion from 

 plain to plateau, was of considerable duration. With 

 the beginning of the uplift, the sluggish streams of the 

 plain became rejuvenated, and took up actively once 

 more the work of erosion. By the time the maximum 

 uplift was reached, the plateau had lost to a certain 

 degree its character of extreme levelness. The streams 

 had already entrenched themselves in rather conspic- 

 uous valleys. It is believed that the great volcanoes 

 of Washington Rainier and its associates began 

 their activities about . the time the uplift described 

 above reached its maximum height. In the vicinity 

 of Rainier the rock of the old plateau is granite ; and 

 the volcano may be said to be built upon a platform 

 of that material. On the north side of the mountain 

 granite appears conspicuously at a height of about 7,000 

 feet ; while on the south side it appears at points varying 

 from 5,000 to 6,000 feet above the sea. 



That the surface of the granite platform was irregular 

 and uneven may be seen in the walls of the Nisqually 

 canyon, near the lower terminus of the glacier. As one 

 ascends the canyon to the glacier, the contact between 

 the lava rock and the granite shows quite plainly on 

 both the right and the left side. On the left the contact 



196 



