946 THE JOURNAL OF GEOLOGY. 
through the rock and are not very numerous. They are very 
minute and cannot be more definitely identified. The ground- 
mass carries irregular patches of light brown mica, small pheno- 
crysts of augite and of serpentinized olivine, and still fewer 
larger crystals of augite and olivine, but none of labradorite. 
The rock is a leucite-bearing modification of shoshonite magma, 
without noticeable difference in the chemical composition. 
The rock of analysis 4 forms a narrow dike on the ridge 
northeast of Indian Peak, Crandall Basin. It is gray and apha- 
nitic, with abundant small phenocrysts of augite and lime-soda- 
feldspar with rather low extinction angles. It is very fine grained 
and holocrystalline, consisting of indistinctly outlined feldspar 
microlites, in part alkaline with low double-refraction and no 
polysynthetic twinning. There is a subordinate amount of 
biotite in idiomorphic microlites, besides prisms of augite and 
grains of magnetite. Olivine is absent, in which respect it differs 
from other varieties of these rocks. Chemically it is very simi- 
lar to the shoshonite from Beaverdam Creek (analysis 2). 
The rock of analysis 5 is the uppermost of five lava sheets 
that overlie one another at Two Ocean Pass. It is dark gray, 
with a waxy luster, and carries scattered phenocrysts of feldspar 
and serpentinized olivine. In thin section the rock is seen to be 
holocrystalline ; the groundmass consisting of orthoclase in idio- 
morphic and also in allotriomorphic crystals, with much magne- 
tite and augite, and some chlorite or serpentine, besides red- 
brown biotite, and hairlike needles of apatite. There are also 
comparatively large, but microscopic, dusted apatites among the 
phenocrysts, showing this mineral in two generations, or periods 
of crystallization. Some of these apatites are enclosed in olivine, 
which is completely serpentinized. The feldspar phenocrysts 
are labradorite, with highly developed polysynthetic twinning. 
In the rock of the second sheet at this place the feldspar pheno- 
crysts are Jabradorite-bytownite, being decidedly basic with high 
extinction angles, and relatively strong double-refraction. The 
groundmass is like that of the overlying shoshonite, just 
described, except that the orthoclase crystals sometimes have a 
