THE GRANITIC ROCKS OF THE SIERRA NEVADA 



161 



159, N. C. is taken from Lindgren's paper in the Seventeenth Ann. Rep., 

 U. S. Geol. Surv., Part 2, p. 45. 



227, S. N. Dike in quartz-mica-diorite (No. 225, S. N.) about 3.2 km. east of 

 Milton in the Downieville quadrangle The dike is about 60 cm. wide. 



171, S. X. Dike in the quartz-mica-diorite about 1 1 km. east of the Sierra 

 Buttes, Downieville quadrangle. The dike is quite wide and is inter- 

 sected by joints, the most prominent set being nearly vertical. 



Pegmatites. — The pegmatites which are associated with grano- 

 diorite and quartz-monzonite are very often banded, the border 



Fig. i. — Boulder of aplite-pegmatite on ridge south of Highland Creek in the 

 Big Trees quadrangle. 



of the dike being aplite and the middle layer pegmatite, thus 

 forming a suggestion of the "comb" structure shown in some 

 quartz veins. In certain cases the banding is repeated, there 

 being several layers of aplite with pegmatite between. This is 



