OF THE UPPER MISSOURI. 117 
main branches unite about thirty miles east of the Black hills, forming the Big Shyenne, 
which empties into the Missouri about sixty miles above Fort Pierre. The Moreau, 
Grand, Cannon-ball, and other rivers flowing into the Missouri north of the Shyenne and 
south of the Yellowstone, rise in a high Tertiary divide north of the Black hills, and are 
for the greater part of the season quite shallow and sometimes nearly dry, but the Little 
Missouri derives a portion of its waters from the Black hills through a number of small 
branches which flow from the northwestern slope. 
We thus see that the Black hills do not give rise directly to any important stream, if 
we except the Little Missouri, a few branches of which flow from springs near the base 
of the hills, but afford a comparatively small supply of water from that source. The Shy- 
enne is fed for the most part from the numerous small streams which issue from copious 
springs in the more elevated portions. It would seem, therefore, that the Black hills do 
not have a marked influence upon the drainage of this region. 
I have already noticed the geological structure of the Black hills, but will state briefly 
its principal points. The nucleus or central portion is composed of a red feldspathic 
granite with a series of metamorphic slates and schists superimposed, and thence upon each 
side of the axis of elevation the various fossiliferous formations of this region follow in 
their order to the summits of the Cretaceous, the whole inclining against the granitoid 
rocks at a greater or less angle. From the above facts we draw the inference that prior 
to the elevation of the Black hills, which must have occurred after the deposition of the 
Cretaceous rocks, all these formations presented an unbroken continuity over the whole 
area occupied by these mountains. ‘This is an important conclusion, and we will hereafter 
see its application to other ranges, and also to the Rocky mountain range taken in the 
ageregate. 
Proceeding in a southwest direction from the Black hills along the anticlinal, we see 
ample evidences of the connection of these hills with the Laramie mountains. By the 
Laramie mountains we designate those eastern ranges which extend from the Red buttes 
southward to the Arkansas. This range when examined in detail is composed of a large 
number of smaller ranges, all, so far as I have observed, of the true granitic type. The 
trend of the whole group is very nearly nerth and south, northward as far as Fort Lara- 
mie, where they make an abrupt flexure around to the west and northwest, and gradually 
cease or die out at the Red buttes. From this point westward and northward, there is a 
space of from twenty to forty miles in width, destitute of mountain elevations, though the 
strata exhibit evidence of dislocation or crust movements. 
Geologically the Laramie range is also composed of a granitoid nucleus, with the fossili- 
ferous formations, Silurian, Carboniferous, Red Arenaceous beds, Jurassic, Cretaceous, and 
in many places Lignite Tertiary, inclining from each side of a central axis at various angles. 
