270 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



observer. It is commonly stated that the glaciation of the 

 Sierra Nevada appears to have been much more recent 

 than in the northern United States. This seems proven by 

 the fresh appearance of some of the moraines and the 

 excellent preservation of the glacial polish high up in the 

 canyons. Until recently, but little attention has been paid 

 to the oldest moraines which occur far down on the flanks 

 of the range and which have been so greatly weathered and 

 covered by vegetation as not to readily attract attention. 

 Moreover, the rocks that lie within the glaciated area near 

 these old moraines never show glacial markings, and are 

 often disintegrated in spots to the depth of twelve to sixteen 

 feet. Yet it is reasonable to suppose that these rocks were 

 hard and ice polished at the time when they were cov- 

 ered with ice. The etching of the granitic pebbles in the 

 Big Meadow moraines west of Yosemite Valley also indi- 

 cates a considerable age, as was first pointed out by Professor 

 Branner. There appears to be no difference, so far as one 

 can judge, between the age of these moraines, as indicated 

 by the amount of weathering displayed, and those of the 

 great continental glacier. When the great glacier of the 

 northern United States retreated, it left a great series of ter- 

 minal moraines extending across the country to the south of 

 the Great Lakes from Long Island through northern Mon- 

 tana, Idaho, and Washington to the Pacific Ocean.' The 

 oldest moraines of the Sierra Nevada may possibly be of the 

 same age as the oldest moraines of this continental glacier, 

 The most recent moraines left by the great glacier in its 

 retreat would, of course, be found further to the north, and 

 it is with these moraines and the corresponding glacial mark- 

 ings that the freshest moraines and markings of the Sierra 

 Nevada should be compared. 



It is still held by John Muir and others that the canyons 

 of the Sierra were cut out by the action of ice. Some 

 writers consider that deep and narrow canyons of certain 

 types are necessarily the work of ice whether evidence of 



1 This terminal moraine is said, however, to represent the second great advance of 

 the continental ice sheet. 



