1 62 H. W. TURNER 



shown in Fig. I. In the more acid dikes or veins (?) the 

 middle band is quartz with aplite borders. 



It is not yet ascertained whether the aplites and pegma- 

 tites occurring in the different granites of the Sierra Nevada 

 show characteristic differences that are constant. ' The oligo- 

 clase-aplite (No. 1730), previously described as coming from 

 the North Mokelumne River, was presumed in the field to be 

 typical of the aplites of the gneisses and biotite-granite ; but 

 it remains to be shown if there is not considerable diversity in 

 these dikes. There are, for example, in the Yosemite quad- 

 rangle, in biotite-granite, sporadic bunches of white platy quartz 

 interspersed with chunks of flesh-colored orthoclase or micro- 

 cline. This forms practically a coarse pegmatite. The quartz 

 in these bunches greatly exceeds in amount the potash-feldspar 

 so far as my observation goes. One bunch of white quartz by 

 the trail to the "Fissures" south of Yosemite Valley is 18 meters 

 long and 14 wide, with chunks of potash-feldspar; but nine 

 tenths of the mass is quartz. Some of the pegmatite in biotite- 

 granite is distinctly banded, 1 the same as in granodiorite. 



H. W. Turner. 



1 Seventeenth Ann. Rep., U. S. Geol. Surv., Part I, p. 700, Plate XXXIV. 



