144 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



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



Si0 2 



per 



No. 



Volcanic rocks of Sepulchre 



Mountain. 



Intrusive rocks of Electric Peak. 





Essential minerals. 











Name. 







Name. 



Essential minerals. 













Phenocrysts. 



Groundmass. 







61.22.. 



272 









pyroxene-mica - dio- 



biotite, hornblende, augite, 



















rite. 



hypersthene, magnetite, 



60. 30 . . 



409 



hornblende- 



pyroxene- 

 andesite. 



hornblende, augite, 

 hypersthene, plagio 

 clase, magnetite. 



glassy, micro- 

 litic. 





plagioclase (quartz). 



58.05.. 



273 































rite. 



hypersthene, magnetite, 



57.38.. 



267 









pyroxene-porphyry . 



plagioclase (quartz), 

 augite, hypersthene, bio- 





















tite, magnetite, plagio- 



57.17.. 



386 



pyr oxene- 

 andesite. 



augite, hypersthene, 

 plagioclase. 



brown glass, 

 microlitic. 





clase, quartz. 



56.61.. 



407 



hornblendc- 

 pyroxene- 

 andesite. 



hornblende, augite, 

 hypersthene, plagio- 

 clase. 



glassy, micro- 

 litic. 







56.28.. 



295 









pyroxeue-mica-dio - 



biotite, hornblende, augite, 



















rite. 



hypersthene, magnetite, 



55. 92 . . 



471 



hornblende- 

 andesite. 



hornblende, plagio- 

 clase. 



microcrystal- 

 line. 





plagioclase, quartz. 



55.83.. 



421 



pyr oxene - 

 andesite. 



augite, hypersthene, 

 plagioclase. 



glassy, micro- 

 litic. 







The effect of this diversity of conditions upon the degree of crystal- 

 lization of the various portions of these rocks is well shown in the accom- 

 panying- Table XVII, which has been derived from Tables VIII and XIII. 



In this table are presented all of the specimens from Sepulchre Moun- 

 tain and Electric Peak. They are arranged in four principal divisions: 

 First, the breccias and lava flows ; second, dikes and larger bodies intruded 

 in these breccias; third, dikes in the Cretaceous strata of Electric Peak; 

 fourth, the main stock and its immediate apophyses. These groups are 

 still further subdivided into columns which correspond to mineralogical 

 differences in the rocks, and bear the same letters as the mineralogical 

 subdivisions in Tables III, VIII, XI, and XII. Consequently each of 

 the four principal groups has the most basic members at the extreme left 

 and the most acid ones at the extreme right. The mineralogical range is 

 therefore repeated four times. The table illustrates a number of facts. It 

 exhibits the relative degree of crystallization of the breccias, lava flows, 



