THE GRANITIC ROCKS OF THE SIERRA NEVADA 151 



The granodiorite analysis may be regarded as typical of that 

 rock and as representing the average rock of many areas. The 

 analysis is the mean of the five analyses given in the large table. 

 A comparison with the banatite analysis indicates a close rela- 

 tionship, but a granodiorite very seldom attains so high an alkali 

 content as that of a banatite. The banatite analysis is a mean of 

 five analyses by Brogger. 1 The analysis of the adamellite is a 

 mean of six analyses by Brogger. 2 The quartz-monzonite analysis 

 103 Pyramid Peak is Lindgren's typical granodiorite of his latest 

 paper. 3 It is clear that this rock would be placed with the mon- 

 zonites by Brogger. 



Granodiorite when typical is composed of plagioclase (oligo- 

 clase-andesine, but usually andesine) > quartz > orthoclase. 

 Biotite and green aluminous amphibole are abundant constituents, 

 but are variable in their relative amounts, and at times only one 

 of these ferro-magnesian elements is present. Magnetite, titanite, 

 and apatite are nearly always present as accessories. The rock 

 is usually evenly granular in texture and of a light gray color. 



QUARTZ-MONZONITE 



As has already been stated under granodiorite, there are 

 very large areas of a rock containing amphibole and biotite which 

 resembles granodiorite and perhaps may be related to it genet- 

 ically. From the analyses given below it will be seen, however, 

 that the rock is richer in alkali and poorer in lime than the most 

 acid of the granodiorites of the Gold Belt. This rock forms 

 part of the east wall of Yosemite Valley and Half Dome, North 

 Dome, Starr King, and other points. In general it is quite mas- 

 sive and thus lends itself to a method of weathering called 

 exfoliation, which ordinarily results in the production of dome- 

 like forms. It is composed of oligoclase>> quartz> orthoclase>- 

 biotite> amphibole. There are present as accessories titanite, 

 apatite, iron ore, and zircon. It thus strongly resembles grano- 



1 Die Eruptionsfolge der triadischen Eruptivgesteine bei Predazzo, p. 62. 



2 Ibid., p. 62. 



'Am. Jour. Sci., 1897. 



