ABSAROKITE-SHOSHONITE-BANAKITE SERIES. 943 
thin prisms of feldspar, frequently grouped in fan-like clusters. 
They are not distinctly striated, and are probably orthoclase. 
Others are lime-soda-feldspars, with low extinction angles, and 
some are irregularly bounded and are obscure. This matrix is 
crowded with idiomorphic crystals of pale green augite, dark 
brown biotite and magnetite. Some of the biotite crystals are 
long, narrow plates, resembling prisms of hornblende, for which 
mineral they were at first mistaken. There is considerable ser- 
pentine scattered through the rock. 
Mineralogically this rock is very similar to the dike rock 
south of Clarks Fork River. Chemically, it is slightly higher in 
alumina and potash and lower in magnesia and lime. The high 
loss on ignition is probably due in this case to the serpentiniza- 
tion of the olivine. 
There are other rocks of this class in the region, but they 
will not be described here. Transitional varieties between 
absarokite and normal basalts occur, as well as transitions to 
shoshonite. 
SHOSHONITE, 
The rocks classed as shoshonites are more numerous 
than the absarokites, and embrace a somewhat wider range of 
composition. They occupy the middle ground, as it were, in 
the series and pass by transitional varieties into absarokite, 
banakite and into normal basalt. They occur associated with 
absarokite, and consequently at the same localities: on the 
Lamar River, Mirror Plateau, Crandall Basin, at various locali- 
ties in the Absaroka Range, and at Two Ocean Pass, one of the 
divides at the head of Shoshone River. From this locality the 
rock was first collected and identified as an orthoclase-bearing 
basalt. Shoshonites also occur in the northwestern portion of 
the Yellowstone Park. Most of these rocks are characterized 
by prominent phenocrysts of labradorite, together with those of 
augite and olivine. But some are without megascopic pheno- 
crysts and are correlated with the porphyritic forms on chemical 
as well as mineralogical grounds. A small number are leucite- 
bearing. 
