64 glXcial and sueface geology of the pacific coast. 



an amphitheatre lying between Bald Mountain and Mount Agassiz. The 

 average height of the basin is 10,000 feet, and the altitude of the two peaks 

 named respectively 11,077 and 13,000 feet. 



Farther east, in the Rocky Mountains proper, the character and extent of 

 the former glaciation of the ranges is now pretty well understood, chiefly 

 owing to the labors of the Geological Survey, under Dr. Hayden's direction. 

 The entire aspect of the conditions closely resembles that furnished by Cali- 

 fornia ; everywhere in the highest ranges, under favorable topographical 

 conditions, glaciers have formerly existed, and have extended down the 

 slopes of the mountains in the cartons to very considerable distances. Al- 

 though they have now entirely disappeared, with the single exception already 

 noted in the Wind River Range, they have left behind them abundant proofs 

 of their past existence in the usual form of moraines, polished and striated 

 surfaces, and i-oches moutonnees, similar to those already described as occurring 

 so extensively in the Sierra Nevada. As in that range, so in the Rocky 

 Mountains, these remains of tlie work of former glaciers exist, not only on a 

 grand scale, but in the greatest perfection ; so that, to the eye of the experi- 

 enced observer, there can Ije no mistake about the nature of the phenomena. 

 There need be no difficulty in separating the results of aqueous from those 

 of glacial erosion, and no reason why, in time, the precise limits of the area 

 formerly covered by ice should not be laid down on the map, just as is now 

 doing for the Swiss Alps. 



At present the northern portion of the Cordilleras is that in regard to 

 which definite information is most to be desired. The ranges, as a whole, 

 decidedly diminish in altitude in that direction; but this falling-off is, to some 

 extent, compensated by the increased latitude. 



In the region of South Park, and especially in the Upper Arkansas Valley, 

 the glacial features are perhaps more striking than anywhere else in the 

 Rocky Mountains. From all the canons of the Sawatch Range, on the west 

 side of the head of tlie Arkansas, large glaciers came down, and have left 

 great morainic accumulations, which extend across the valley in long parallel 

 lines several hundred feet high. The most conspicuous of these moraines are 

 those bordering Pine, Clear, and Lake Creeks. The Twin Lakes, nearly at 

 the head of the valle^y, are enclosed between detrital piles of which the 

 glacial origin cannot be mistaken. The highest adjacent summits on the 

 west are a little over 14,000 feet in heiu-ht, the Sawatch being the most 

 elevated range of the Rocky Mountains ; hence the great development of 



