312 The American Geologist May, isoo 
result of the analyses will be given in the next paper. In hy- 
drochloric acid fragments of the dark mineral first mentioned 
afford gelatinous silica, and an odor of sulphur, the latter 
doubtless from some particles adherent from the other minerals. 
Chromium also is present, and a large amount of magnesia. 
The mineral approaches olivine or bronzite, and appears to be 
only a ferruginated condition of the glassy-yellow mineral. 
In thin section the yellowish mineral is transparent. It pre- 
sents the roughened surface seen on thin sections of olivine, 
but it has not its brilliant polarization, in the latter respect 
resembling bronzite. It is intersected irregularly by fissures 
in which is gathered a ferruginous product of decomposition 
(limonite), and which increase to so great an extent that in 
some places, the section is nearly opaque, showing a gradation 
from the black-opaque mineral mentioned to this yellowish 
glassy one, and indicating their original identity. 
Besides these transparent polarizing minerals there may be 
seen two that are always and entirely opaque. One is black 
as above, and may be the one that contains the chromium al- 
ready detected, but the other is brassy. The former may be 
chromite or daubreelite and the latter troilite. 
[To be contiuuecl.j 
REVIEW OF RECENT GEOLOGICAL LITERATURE. 
Report of the School of Mines of Colorado, 8vo pp. 264. We have re- 
ceived from Prof. Arthur Lakes, state geologist of Colorado and one 
of the editors of the American Geologist, a copy of his annual report 
for 1889 containing a narrative of the exploration of the coal deposits of 
that state during the preceding year. It opens witli a cliapter on the 
natural history of coal in which the author points out that though the 
coal supply of Colorado is not of Carboniferous but of Cretaceous age 
and consequently much younger than that of the eastern states, yet it is 
of good quality. This is not, he says, generally believed. "We have an- 
thracite as good as that of Pennsylvania, bituminous coals in beds of 
great thickness comparing favorably with that of the east and of such 
remarkable purity that it will yield coke as good as that of the far 
famed Connellsville lield." "If the western states had been discover- 
ed first and had become as thickly populated as the eastern states now 
are, it is a question whether Colorado, Wyoming and adjacent territor- 
ies would not have been considered the great coal-area of the U. S." 
On the resources of the far West he says: "At least 20,000 sq. miles 
