THE GRANITIC ROCKS OF THE SIERRA NEVADA 1 



The higher part of the central Sierra Nevada and nearly the 

 entire width of the southern Sierra consist of a granular 

 complex to most of which the name granite is ordinarily applied. 

 In the northern and central part of the range there are likewise 

 numerous isolated granitic areas enclosed in rocks of other kinds. 

 The rocks of the granular complex differ greatly in age and in 

 chemical composition. The oldest rocks represented are gneisses. 

 Some of these are probably recrystallized sediments, but the 

 larger portion of them may be of igneous origin. While differ- 

 ing in origin these gneisses are a unit in that they have all 

 undergone a thorough recrystallization under great pressure. 

 While the associated granites may be in part responsible for this 

 recrystallization it cannot be ascribed to contact metamorphism 

 alone, for areas miles in diameter are as thoroughly crystalline 

 in their middle portions as at the granitic contact. At a future 

 time these gneisses will be described. Some notes regarding them 

 may be found in the Seventeenth Annual Report of the United 

 States Geological Survey and in the text of the Big Trees folio. 



The granolites 2 of the Sierra Nevada comprise nearly the 

 entire range of granular igneous rocks. Peridotite, pyroxenite, 

 hornblendite, gabbro, diabase, diori.te, syenite, monzonite, and 

 granite, with various intermediate types, are all represented. In 

 this paper, however, reference will be made only to the granitic 



' Published by permission of the Director of the U. S. Geological Survey. A 

 large amount of information has been accumulated about the granular complex of the 

 Sierra Nevada. It is thought better, however, to delay the publication of this material 

 until the field work now under way is completed. There is some confusion in regard 

 to the biotite -granite of the range and the granodiorite and quartz -monzonite. They 

 are, therefore, more fully treated than other types of which only a brief statement is 

 presented here. 



2 The term granolite is here used for all granular igneous rocks ; thus diorite, 

 gabbro, syenite, and granite would all be called granolite. It was first suggested by 

 Professor L. V. Pirsson. 



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