FORMER GLACIATION OF THE SIERRA NEVADA. 33 



party, spent the summer of 1869 on the highest portion of the Kocky Moun- 

 tains, near South Park, and on the western side of the head-waters of the 

 Arkansas River. During the months of July and August of that year there 

 were never as many as three consecutive days without rain, and only rarely 

 as many as two. The rain-fall was quite tropical in character, beginning 

 about noon, and usually lasting until evening, with occasional violent showers. 

 In some instances snow fell on the summits of the highest peaks ; but as 

 a general rule the precipitation did not seem to extend up as high as 

 that. Thunder and lightning, sometimes very severe, almost invariably 

 accompanied these rain-falls. In spite of the great number of rainy days, 

 however, the ground was never more than superficially wet, evapox'ation tak- 

 ing place with the greatest rapidity, and the whole aspect of the Arkansas 

 Valley was that of a dry country. 



Nowhere on the higher portions of the ranges adjacent to South Park was 

 anything seen approaching a glacier in character. There were patches of 

 snow, sometimes of many acres in extent, in sheltered nooks, and in depres- 

 sions on the northern slopes of the higher peaks. The ainount of snow 

 remaining through the season did not appear to differ much from the average 

 quantity left on portions of the Sierra Nevada of corresponding elevation, 

 and in the same latitude. 



Having thus given a general view of the present condition of the Cordil- 

 leras with regard to the occurrence of snow and ice, we shall now be pre- 

 pared to discuss the phenomena of former glaciation in the same region. 

 From what has been said in the preceding pages, it will be evident that, at 

 the present time, there are no glaciers within the limits of the United States 

 possessing any considerable significance as geological agents. It is only at 

 some distance north of our territory and along the Pacific Coast that what 

 may be properly called a system of glaciers occurs, and which, although up 

 to this time only very imperfectly explored, is undoubtedly attended by the 

 usual interesting accompaniments of the formation of moraines and other 

 glacial phenomena on a large scale. But, as already suggested, there has 

 been in former times a very extensive development of glaciers, not only in 

 the Sierra Nevada, Init in the Rocky Mountains also, while indications of their 

 former presence are not entirely wanting in the ranges of the Great Basin 

 itself For convenience of description we may begin with the most southern 

 portion of the Sierra Nevada at which traces of former glaciation have been 

 observed, and, following the range northward, give such particulars as have 



