942 THE JOURNAL OF GEOLOGY. 
ence of leucite in similar rocks in this region render this highly 
probable. Some parts of the rock contain what is undoubtedly 
analcite. The occasional large quartz crystals have the charac- 
ter of primary crystals. Their possible association with leucite 
is indicated, but no leucite has been actually observed in the 
rock. 
This rock resembles the dike rock from the divide at the head 
of Lamar River in the general character of the groundmass, 
except that the phenocrysts of olivine and augite are almost 
microscopic, and may be considered as part of the groundmass. 
The ferromagnesian minerals are about the same in each, and the 
feldspathic components are obscure, with indications of alkaline 
character. 
The rock of the lava flow at the head of Raven Creek is dark 
gray with abundant small megascopic phenocrysts of olivine and 
augite. In thin section these minerals resemble those in the 
rocks already described. The groundmass consists of small rec- 
tangular prisms of orthoclase, sometimes with minute cores of 
prismatic labradorite; besides abundant microscopic crystals of 
augite and magnetite, there is a little serpentine. The feldspars 
are distinctly crystallized and their character as orthoclase is 
unquestionable. They resemble the orthoclase in the leucite- 
absarokite from Ishawooa Canyon. No leucite, however, was 
observed in this rock. Only avery small part of the groundmass 
is lime-soda-feldspar. There is no biotite, and no analcite. Apa- 
tite occurs in delicate needles. The absence of biotite may be 
correlated with more pronounced orthoclase and abundant 
olivine; and the absence of leucite accords with the higher per- 
centage of silica. 
The rock, whose composition is shown by analysis 5, occurs 
as a narrow dike on the divide east of Cache Creek. It 
is brownish gray and aphanitic, without phenocrysts, but hav- 
ing minute brown pseudomorphs, presumably after  oli- 
vine. There are occasional rounded grains of dark colored, 
crackled quartz, surrounded by a thin, green shell. In thin sec- 
tion the rock is fine grained and holocrystalline, consisting of 
