OF THE UPPER MISSOURI. 21 
sesses a more laminated and arenaceous structure, sometimes approaching to a calcareous 
sandstone. 
Leaving this locality, we continue to pass over No. 5, and scattered over the surface of 
the ground are numerous fossils, loose or in argillaceous concretions, as Jnoceramus, Bacu- 
lites, Ammonites. About five miles north of our last night’s camp, near the source of the 
south fork of the Shyenne, a few beds of the lignite Tertiary basin were observed. 
1. Yellow arenaceous bed, holding the same position, I think, as the one at Fort Clark, which contains numercus 
freshwater shells. 
2. Light gray grit, with numerous iron rust concretions, same bed seen on Cherry creek, at Fort Clark, on the 
Missouri above Fort Union and on the Yellowstone. 20 to 30 feet. 
3. Very impure lignite. 4 to 6 feet. 
4. Dark ash-colored clay passing up into lignite. 20 feet. 
5. Fine yellow sand about 6 feet exposed. 
These Tertiary beds rest conformably upon cretaceous formation No. 5, and no disturb- 
ance was observed in this locality. 
Crossing the Shyenne on our way northward, we have the commencement of a series of 
ridges of upheaval, which surround the Black hills. As we approach the southern base 
of the Black hills, the strata dip very nearly to the southeast. No. 1 does not appear, 
but we have a tine development of No. 2, possessing its usual characters, a plastic clay 
with ash-colored arenaceous concretions and an abundance of well-preserved fossils. No. 
3, with large quantities of O. congesta, and J problematicus, in an exceedingly comminuted 
condition, No. 4 also appears, and No. 5 caps the hills on all sides. Nos, 2 and 3 are 
revealed only by the upheaval. On a branch of Beaver creek we find No. 2 one hundred 
and fifty to two hundred feet in thickness, and exhibiting its lithological characters in 
full; first, the summit is composed of ferruginous and gray laminated sandstone containing 
L. problemuticus and fragments of fishes, seeming to form a bed of passage from No. 2 to 
No. 3, 6 to 10 feet in thickness ; then, alternate thin layers of gray sand and black shaly 
clay, with an occasional seam one inch to six inches in thickness of ferruginous sandstone, 
the whole passing down into a black plastic clay, precisely like that which forms No. 2 on 
the Missouri river. 
We ascend, therefore, to the Black hills by a series of steps or upheaved ridges gradually 
increasing in height as we approach the central ridge, and the strata more nearly approach- 
ing a vertical position. ‘The first step or ridge is, perhaps, fifty to eighty feet in height, 
revealing Nos. 4 and 95; the second shows Nos. 4 and 3; third, Nos. 3 and 2, and so 
through all the series of strata until we come to the Potsdam sandstone resting uncon- 
formably upon the metamorphic rocks. 
