FOR^^IER GLACIERS AT THE HEAD OF THE STANISLAUS. 53 



of similar origin in the Upper Arkansas Valley. It was also remavked that 

 here, as in most cases in the Rocky Mountains, the lateral moraines high up 

 in the range seem to have been almost entirely obliterated, while those low 

 down, on the nearly level valley, at the base of the mountains, are not only 

 of immense size, but perfectly preserved in form. 



Passing to the north of the Tuolunme River, we find a very considerable 

 change in the topography of the Sierra, accompanied by a rapid decline in 

 its altitude. These altered conditions make themselves manifest at once 

 in the character of the traces of former glaciation which are discoverable. 

 There are no more such immense ancient glacial systems as those of the 

 King's and Tuolumne rivers, which rival with or even surpass the largest 

 ice-fiows at present existing in the Alps. This is as we should exjject, for the 

 traces of former glaciers are everywhere in the Sierra Nevada found to be 

 in strict harmony with its present climatic and topographic features. From 

 the head of the Tuolumne north there is no longer one almost unbroken 

 western slope to tlie range, Avith an extremely rapid descent on the east into 

 a deep valley, separating the Sierra Nevada most distinctly from the Great 

 Basin ranges ; the mass becomes more and more split up into subordinate 

 parts by spurs making off to the north and inosculating with still more 

 easterly ranges, so that any line of division between them must be largely 

 artificial. Finally, when we reach Plumas County we have several nearly 

 parallel ranges of about equal elevation, enclosing extensive valleys, where, 

 however, the elevation is not great enough to have given rise to large gla- 

 ciers, and where the diminished precipitation also makes their former exist- 

 ence less probable. 



Another circumstance renders the conditions of the northern portion of 

 the Sierra less favorable than they are farther south for the observation 

 of the traces of former glaciation. The farther we go north the more the 

 higher portions of the range become covered with volcanic materials, which 

 are almost entirely wanting about the upper basins of the large rivers of the 

 High Sierra. These volcanic rocks are not fiivorable either for receiving or 

 retaining glacial striation or polish. 



The next stream of importance, north of the Tuolumne, is the Stanislaus, 

 and the range of the Sierra at its head is still quite high, the Sonora Pass, 

 which leads from the head-waters of the Stanislaus to those of the West- 

 Walker River, being about 10.000 feet above the sea-level. But glacial 

 markings were not seen on the eastern slope of the pass at a distance from 



