404 GEOLOGY OF THE EUREKA DISTRICT. 



PLATE VII. 



1. PHENOCRY8TS OF BLACK BORDERED HORNBLENDE AND PLAGIOCLASE FELDSPAR IN HORNBLEXDK- 



BEADING PYROXENE-ANDESITK. 



Thin section 77, magnified 50 diameters. The glass inclusions in the feldspars and tho feldspar micro- 

 lites in the groundmass are shown. 



2. BASALT. 



Thin section 257, magnified 225 diameters. The lath-shaped plagioclase and magnetite grains are dis- 

 tinctly shown, but the augite is not well defined. 



