214 
IDDINGS. 
blende-mica-andesites, 2736, 394, are the equivalents of 
the quartz-mica-diorites, 3008, 2724, 2695, 2668, 2676. 
The dacites, 3017, 3680, are the equivalents of the quartz- 
mica-diorite-porphyrites, 3001, 2670. The hornblende- 
pyroxene-andesites and pyroxene-andesites, 219, 694, 214, 
221, 217, are the equivalents of the coarse grained diorites, 
2669, 2692, and of fine grained facies, 2679, and they 
resemble certain porphyrites occurring in sheets, one of which 
is a hornblende-porphyrite, 2089, and the other a horn- 
blende-mica-porphyrite, 154. 
The dacites and hornblende-mica-andesites included 
within this correlation are intruded bodies within the brec¬ 
cia of Sepulchre Mountain, and have the same mineral com¬ 
position as the corresponding porphyrites and diorites of 
Electric Peak. They differ from them in structure and de¬ 
gree of crystallization, the details of which cannot be de¬ 
scribed in this paper. 
The glassy andesites with pyroxene and hornblende 
phenocrysts, however, present the utmost contrast to the 
equivalent coarsely crystalline diorites. In the former the 
hypersthene, augite, hornblende, and plagioclase are sharply 
defined, idiomorphic crystals of these minerals, scattered 
through a groundmass of glass, which is crowded with mi- 
crolites of plagioclase and pyroxene besides grains of mag¬ 
netite. The hornblende is brown, occasionally red, and the 
other phenocrysts have all the microscopical characters which 
distinguish their occurrence in glassy rocks. In the diorite 
the hornblende is green, in some cases brown; the hyper¬ 
sthene, augite, and hornblende are accompanied by biotite, 
and are all intergrown in the most intricate manner, with 
evidence that they commenced to crystallize in the order 
just given. The labradorite is often clouded with minute 
opaque particles, which are characteristic of its occurrence 
in many diorites; it is surrounded by a shell of more 
alkaline plagioclase, which, with occasional individuals 
of orthoclase and considerable quartz, closed the crys¬ 
tallization of the magma. Magnetite, apatite, and zircon 
