1884.] Geology and Paleontology. 527 
tals. Microscopically this rock is seen to be composed of ledge- 
agioclase, irregular grains of light brownish-green augite, 
colorless olivine, magnetite, and glass. The hypersthene andesite 
is generally a porous, sometimes pumiceous, rock, varying in color 
from blue-black to steel-gray, but sometimes red or reddish-gray. 
Inclosed in the ground-mass are numerous porphyritic feldspar 
crystals, with some augite and hypersthene. Microscopically the 
rock is seen to be composed of plagioclase, augite, hypersthene, 
magnetite, and a glassy base sometimes globulitic, more often 
filled with microlites of feldspar and pyroxene, and magnetite 
grains. The hornblende andesite is arranged into two varieties: 
one near the hypersthene andesite, and resembling it in appear- 
ance and structure, but contains hornblende; the other consists. 
chiefly of ledge-formed feldspars, minute pyroxenes, a little 
magnetite, with or without colorless glass, all inclosing porphy- 
ntic plagioclases and hornblendes. 
_ 4he most interesting rock described is the dacite. This name 
given to the rock styled by Richthofen, in 1867, xevadite or 
granitic rhyolite, of which Mr. C. King declared, in 1878, that it 
was “entirely made up of crystalline minerals, with only the 
slightest traces of vitreous binding material.” He also classed it 
with the thyolites, In 1881 the present writer pointed out that 
‘ait was mistaken in his statements of the small amount of glass,. 
ya referred the nevadite to the trachytes. 
as ague and Iddings say that they can not regard the rock as in 
ec entitled to be classed as a rhyolite, and that it is rich 
hara T base, so far agreeing with the present writer; but they- 
of ot under dacite (meaning a quartz-bearing andesite), a term: 
ich he fails thus far to see any need in lithology. Our au- 
k seem inclined to carry the term andesite in ite subdivisions 
dent at extreme that Zabó does the word trachyte—a not 
ansan proceeding on their part. The analyses that have been 
batisá po indicate that nevadite belongs to the trachytes, 
i iiaa to the andesites. ‘It is described by Messrs. Hague and 
through "yee amg of a colorless glass full of gas cavities, 
plagioclase ich are found relatively few microscopic crystals of 
zircon, fo » hornblende, mica, pyroxene, magnetite, apatite and. 
rming a ground-mass inclosing plagioclase, mica, horn- 
quartz, and rarely pyroxene. 
majority of 1 of Messrs. Hague and Iddings is in advance of the 
the cp, oo ee ones, inasmuch as it attempts to describe 
regarding oa not look upon them as small mineral cabinets, 
find thet - a few of the pretty minerals enclosed. Our authors 
al a ui above described rocks grade into one another— 
inthe pa. Orms existing between any two types—a view that, 
