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Sierra Club Bulletin 



stream, what manner of rocks might be expected in the 

 moraines and what particular branch of the glacier had trans- 

 ported them. On the other hand, it sometimes happened that 

 the physiographer, upon entering a new district, would notice 

 in the moraines fragments of a new rock type, and thus was 

 able to predict the existence of a certain formation in the 

 region whence the ice had come. The two men thus carried 

 on team work of a mutually profitable sort. 



That the identification of the disintegrated older moraines 

 was not always an easy matter, may readily be surmised. The 

 rocks of the Yosemite region unfortunately are almost ex- 

 clusively granites, popularly speaking, that is, crystalline 

 igneous rocks closely allied to each other and not greatly dif- 

 fering in general aspect, at least not to the untrained eye. 

 When thoroughly weathered these rocks look much alike. As 

 a consequence the physiographer was at times obliged to stop 

 his pacing and spend an hour with his geological hammer 

 breaking pebbles and chipping corners off boulders in order 

 to discover one of the desired diagnostic types. Such work, 

 however, although it consumed much time, usually yielded 

 gratifying results. An afternoon of rock breaking on Glacier 

 Point established once and for all the fact that that promono- 

 tory has been overwhelmed by the ice of an early epoch — an 

 epoch so early that except for some boulders and cobbles en- 

 cased in residual soil in a protecting hollow, all sign of the 

 ice flood has long since disappeared. Yet the evidence is in- 

 disputable, many of the cobbles unearthed and broken prov- 

 ing to belong to rock types from the Little Yosemite region 

 and foreign to the Glacier Point neighborhood. It may be 

 said in passing that the basin-shaped hollows in the bare rock 

 surfaces of Glacier Point are not pot-holes produced by 

 streams under the ice, but are merely the result of rapid 

 disintegration of the rock in particularly vulnerable spots. It 

 is certain that the ice did not leave these depressions, for there 

 is ample evidence in various localities showing that since the 

 early ice flood which visited Glacier Point the surface of the 

 rock has been removed to the depth of several feet from 

 bare, unprotected places of this sort by the slow processes of 

 disintegration. 



