FOEMEE GLACIATIOX AT THE HEAD OF THE MOKELUJUNE. 55 



been cleared of the overlying detritus by those engaged in washing for gold. 

 Nowhere can a trace of the former existence of glaciers in this reo-ion be 

 discovered. Indeed, there is not a locality in the. Sierra where any proof 

 whatever has been obtained that the ice descended, even in the most favor- 

 able positions, to a point as low as 2,000 feet above the sea-level. And a 

 large extent of rock-surface has been exposed, all through the auriferous belt, 

 by the various and extensive mining operations there carried on. 



The Mokelumne River heads in a group of high peaks six miles south of 

 Silver Mountain ; the eastern slope is drained in this part of the range by the 

 head-waters of the Carson. Numerous branches of the South Fork of the 

 American River take their rise in the northwestern slopes of the spurs whose 

 opposite sides drain into the Mokelumne. The Cosumnes River, wliieh runs 

 into the Sacramento between the Mokelumne and the American, does not 

 head so far up as the summit range of the Sierra. This stream need not, 

 therefore, be taken into con.sideration in describing the foi'mer glaciation of 

 the region. The Mokelumne, also, is of little importance in this connection ; 

 for, although its sources drain an elevated district, there are no important 

 affluents coming into it at high altitudes, so that there was no chance for 

 the formation of a large glacier at its head. The lowest point in this region 

 at which evidences of the former presence of ice were detected was Silver 

 Valley, 7,300 feet above the sea-level. This locality is in the Stanislaus 

 Valley, about twenty-two miles from the Calaveras Big Trees, on the road 

 to Silver Mountain. At Hermit Valley, on the Mokelumne, at an altitude 

 of 7.259 feet, distinct marks of o;lacial action were met with, and from this 

 point they continued to l)e observed in abundance almost up to the very 

 summit of the pass, the height of which is nearly 9.000 feet above the sea- 

 level. No extensive moraines were seen ; but it can hardly be doubted that 

 a sufficient amount of detailed exploration in this region would make it 

 possible to lay down the ancient limits of the ice with considerable approach 

 to accuracy. The thickness of the mass must have been great in this region, 

 just in the vicinity of the sunnnit, for large blocks of granite may be seen 

 on the crest of a ridge, about 300 feet high, a little south of tlie pass, resting 

 on the lava in a position such as the}' could not have taken without the help 

 of ice. As already suggested, in regions like this, where friable and easily 

 disintegrated volcanic rocks abound, the amount of erosion whicli has taken 

 place since the melting away of the ice is quite considerable, rendering it 

 difficult to connect the isolated occurrences of transported material Avithout 



