140) 
PROCEEDINGS OF THE ACADEMY OF 
I. Granitic and Metamoephosed Azoic Rocks. . 
From the month of the Platte to Fort Laramie we meet with no indications 
of those disturbing influences from the subterranean forces which have wrought 
such changes in the physical features of the country in the vicinity of the 
mountain chains. But proceeding north and west from Fort Laramie, we soon 
find the different formations, older than the Tertiary, distorted and dipping at 
various angles. We observe, at first, a series of elevations in the form of 
isolated conical hills with rounded summits, varying from fifty to two hundred 
feet in height, for the most part, capped with Carboniferous limestones, which 
incline at various angles from 5*^ to 30°. Toward the main axis we find the 
elevations in the form of oblong ridges, frequently interrupted by narrow 
valleys, and presenting a full series of the formations known in this region, from 
the granite to the carboniferous limestones. 
Winding around these conical peaks and ridges are numerous streams of 
pure water, margined with birches, poplars, and other trees, of the same species 
as those found in far northern latitudes. Not unfrequently the valleys formed 
by these streams are of considerable width, with a soil composed of the debris 
of the granitic and metamorphic rocks which sustains a quite luxuriant growth 
of vegetation. Laramie Peak,* the highest elevation in the Laramie range of 
mountains, is composed mainly of a coarse red feldspathic granite, surrounded 
by a series of azoic strata composed of gneiss, hornblende, micaceous and 
clay slates and quartz more or less pure, standing vertical, and inclining 
against the older granitic rocks. Raw Hide Peak, which is alsout 1,000 feet 
high, is also composed principally of granite which has been protruded upward 
through the overlying rocks, while all around the base of the peak, in regular 
sequence outward, may be seen the different azoic strata in a nearly or quite 
vertical position. Proceeding northward from Fort Laramie, the granitic and 
metamorphosed rocks cease to appear after passing the head of the Niobrara 
river, and from thence to the Black Hills we observe only slight local distur- 
bances, sufiicient to expose the Cretaceous beds down to No. 1, but showing 
most conclusively that the same subterranean forces that elevated the Laramie 
Mountains, raised the Black Hills also. 
Arriving at the base of the Black Hills, we ascend by a series of stair-like 
ridges to the central or highest portion, and find that it is composed of a similar 
coarse red feldspathic granite as a nucleus, with a series of azoic strata resting 
against the granite. At the foot of the Black Hlls, Cretaceous bed No. 5 is but 
slightly disturbed ; dipping, perhaps, at an angle of 5°, and forming the first of 
a series of upheaved ridges which surround the principal axis. Passing over 
the first ridge we descend somewhat abruptly into a valley, and gradually ascend 
a second ridge, composed of Cretaceous beds Nos. 5 and 4, from eighty 
to one hundred feet in height, inclining at a still greater angle. The third 
ridge is formed of Nos. 4 and 3, and so on through all the different formations 
to the Potsdam sandstone, which is sometimes nearly vertical, and at others so 
elevated as to hold a nearly horizontal position. The granite of the Black 
Hills contains much more mica than that forming the nucleus of the Laramie 
Mountains, and might perhaps be more properly called a micaceous granite. 
The Black Hills furnish the only examples on our route of the outburst 
of trappean rocks. Stone Peak, on the north eastern side of the Black Hills, is 
an isolated protrusion, composed of every variety, from a most cellular or vesi- 
cular porphyritic lava, to a rather compact rock, which sounds under a blow of 
a hammer like clink-stone. The highest portion of the peak is composed of 
trap rock of greater age than that above described, very compact, contains 
much iron, and assumes the form of pentagonal columns very similar to those 
described in Dr. Owen's report as occurring around Lake Superior. Near Bear 
* Elevation unknown. 
[June, 
