IGNEOUS) ROCKS IN YELLOWSTONE PARK. 
197 
Table II. 
Mineral variation of the diorites and their facies at Electric Peak. 
(a) 
pyroxene 
biotite 
labradorite 
OLIGOCLASE 
quartz 
(&) 
pyroxene 
hornblende 
BIOTITE 
labradorite 
OLIGOCLASE 
quartz 
(c) 
pyroxene 
hornblende 
biotiie 
LABRADORITE 
OLIGOCLASE 
orthoclase 
QUARTZ 
(d) 
hornblende 
biotite 
LABRADORITE 
OLIGOCLASE 
orthoclase 
quartz 
(e) 
HORNBLENDE 
biotite 
• labradorite 
oligoclase 
orthoclase 
quartz 
(/) 
hornblende 
biotite 
oligoclase 
orthoclase 
quartz 
(9) 
biotite 
oligoclase 
ORTHOCLASE 
quartz 
The porphyrites associated with the diorites vary iii min¬ 
eral composition from those with phenocrysts of pyroxene 
and some hornblende, through varieties with hornblende and 
biotite, to those with biotite and quartz, plagioclase being 
common to them all. The series is represented by the 
following table: 
Table III. 
Variation of phenocrysts in the- porphyrites at Electric Peak. 
w 
pyroxene 
(*) 
pyroxene 
hornblende 
M 
PYROXENE 
HORNBLENDE 
(d) 
pyroxene 
hornblende 
b) 
hornblende 
(/) 
hornblende 
biotite 
U) 
hornblende 
BIOTITE 
(h) 
hornblende 
biotite 
(0 
hornblende 
biotite 
U) 
BIOTITE 
quartz 
The variation in the nature and abundance of the por- 
phyritical ferromagnesian silicates is accompanied by a 
gradual change in the character of the plagioclase, which is 
more basic at the pyroxene end of the series; besides a 
