CHEMICAL CORRELATION OF THE ROCKS. 



143 



by faulting and erosion, it is evident that of the different magmas erupted 

 a part found their way into vertical fissures and took the form of dikes ; 

 part reached the surface and became lava flows and breccias, while other 

 portions remained in the conduit. Therefore the various portions of the 

 magmas solidified under a variety of physical conditions imposed by the 

 different geological environment of each, the most strongly contrasted of 

 which were the rapid cooling of the surface flows under very slight pressure 

 and the extremely slow cooling of the magmas remaining within the conduits 

 under somewhat greater pressure. 



Table XVI. — Correlation of the two groups of rocks upon a chemical basis. 



S:.0 2 

 per 

 cent. 



No. 



Volcanic rocks of Sepulchre Mountain. 



Intrusive rocks of Electric Peak. 



Name. 



Essential minerals. 



Name. 



Essential minerals. 













Phcnocrysts. 



Ground mass. 







69. 24 . . 



326 









quartz mica-diorite- 

 porphyry. 



quartz, biotite, plagioclase 

 and alkali feldspar, horn- 

























blende. 



67. 54 . . 



321 









quartz-mica-diorite . 



biotite, hornblende, plagio- 

 clase (orthoclase), quartz. 













67.49.. 



523 



dacite 



quartz, biotite, horn- 

 blende, plagioclase. 



noncrystalline, 

 quartz, feld- 

 spar. 







66.05.. 



323 









quartz-mica-diorite . 



biotite, hornblende, plagio- 

 clase (orthoclase), quartz. 













65.97 



329 









quartz-mica-diorite* 

 porphyry. 



biotite, hornblende, plagio- 

 clase (orthoclase), quartz. 













65.66.. 



521 



dacite 



quartz, biotite, horn- 

 blende, plagioclase. 



holocrystalline, 

 quartz, feld- 

 spar. 







65.60.. 



303 









quartz-mica-diorite . 



biotite, hornblende (pyrox- 

 ene), plagioclase (ortho- 

























clase), quartz. 



65.50.. 



494 



hornblende- 

 mica-ande- 

 site. 



hornblende, biotite, 

 plagioclase. 



holocrystalline, 

 quartz, feld- 

 spar. 







65. 11.. 



311 









quartz-mica-diorite . 



biotite, hornblende, augite, 

 hypersthene, plagioclase 

























(orthoclase), quartz. 



64.85.. 



313 









quartz-mica-diorite . 



hornblende, biotite, plagio- 

 clase (orthoclase), quartz. 













64.27.. 



487 



hornblende- 

 iuica-ande- 

 site. 



hornblende, biotite, 

 plagioclase, mag- 

 netite. 



holocrystalline, 

 quartz, feld- 

 Bpar. 







64. 07 . . 



309 









quartz-pyroxene - 

 mica-diorite. 



biotite, hornblende, augite, 

 hypersthene, magnetite. 

























plagioclase (orthoclase) , 















quartz. 



