42 
PROCEEDINGS OP THE ACADEMY OF 
the disturbed condition of the strata over which he is passing, unmistakable 
evidences that the hills looming- up before him are not merely elevations left 
by the denuda,tion of the surrounding country, but monuments of the former 
action here of those powerful subterranean forces which have played so impor- 
tant a part in modifying the earth's physical features. 
First, in passing from the undisturbed overlying Miocene formation, we come ^ 
directly upon No. 5, or the upper member of the Cretaceous series of the north- 
west, as subdivided in the published sections of the Nebraska formations. Then 
in regular succession Nos. 4, 3, 2, and 1, are passed over, all dipping sometimes 
at a high angle away from the Black Hills.* Beyond, and coming up from be- 
neath No. 1, an older series of very similar strata, containing many organic re- 
mains, which we regard as Jurassic types, is passed over, as we ascend the hills. 
Then we have some fine red gypsum bearing deposites, separated by a bed of lime- 
stone containing a few fossils like Coal measure forms. 
Next comes a group of well-marked Carboniferous formations, which repose 
upon a reddish and grayish sandstone of the same age as the Potsdam sand- 
stone of the New York system, — all of which were often seen highly inclined, 
and apparently conformable. The Potsdam, in its turn, was met with, some- 
with remarks in relation to the Geology of the Black Hills, has been prepared 
for the purpose of being read at the next meeting of the Academy of Natural 
Sciences in Philadelphia, and I therefore, beg leave to ask the authority of the 
Department thus to dispose of it. 
The region embraced by these Black Hills lies mainly between the north and 
south forks of the Shyenne River, and north-west of the well-known Mauvaises 
Terres of White River. Everything relating to it has hitherto been most im- 
perfectly understood. Situated remote from the great lines of travel to the Pa- 
cific, and inhabited by brave and numerous warriors of the Dakota nation, de- 
termined to resist the encroachments or intrusions of white men, it has 
remained an unknown land, especially to scientific men, whose pursuits are 
viewed by the Indians with superstitious apprehension. Even the trappers and 
traders have generally avoided this dangerous locality, and hence the most er- 
roneous ideas have been entertained of the position, direction, extent, and 
formation of these so-called Hills. 
Our exploration of the past year has, however, in a great measure settled 
these points. We now know them to be a detached portion of the great up- 
heaved mountain mass occupying the western portion of the territory of the 
United States, and the most eastern part of it yet discovered. They form an 
assemblage of mountain elevations lying between the meridians of 103° 15, and 
104° 45, west from Greenwich, and between the parallels of 43° 20 and 44° 45 
north latitude, the general deviation of the upland being about N. 20® W. The 
highest peaks are elevated about 6700 feet above the level of the sea, and from 
500 to 4500 feet above the surrounding country. 
The geological discoveries which the exploration has made are of much value 
to science, and the announcement of a few of the most important ones is the 
object of the paper herewith submitted. Mr. Meek has co-operated with Dr. 
Hayden in elaborating the results from the materials collected, without any 
pecuniary recompense from the government, Dr. Hayden being the Geologist to 
the expedition. Very respectfully your ob't serv't, 
G. K. Warren, Lt. Top. Engrs. 
The above letter, and accompanying paper, have been submitted to the Secre- 
tary of War. Their communication to the Academy of Natural Sciences is 
authorized. A. A. Humphreys, 
March 1, 1851. Capt. Topi. Engrs. in charge of Office &c. 
* We should state here that the Tertiary beds were also often seen in the form of out- 
liers, reposing uncon form ably on several of the older rocks, even down to the Carbon^ 
iferous, near the south base of the Black Hills. 
[March^ 
