OF THE UPPER MISSOURI. 15 
thickness of loose material, but that Pliocene beds form the base. The middle portion is 
Post Pliocene, and on the top from fifty to one hundred feet of loose incoherent sand. 
August 2d. There are very few exposures of the different beds in the valley of the 
main branch of Loup fork, but fifteen miles south of our road towards the Platte, a 
branch of the Loup fork seems to pass between nearly vertical banks. One of them ex- 
hibits a section which shows the Pliocene character of the beds: 
1. Yellowish-brown grit. 
2. Whitish chalky stratum containing many freshwater shells. 3 feet. 
3. Heavy-bedded gray grit. 8 to 10 feet. 
From this point to the head of Loup fork the geology of the country is similar, consist- 
ing of sandhills and recent Tertiary beds. The true Tertiary beds are concealed for the 
most part by superficial deposits, a few places only being exposed by denudation. From 
these 1 was able to collect some interesting vertebrate remains, as a new species of Masto- 
don (M. mirificus), Hipparion, Cervus, Elephas, &c. The whole of this portion of the 
country may be regarded as a desert, nearly destitute of wood and water. From the head 
of Loup fork we pursued a northwest course to the Niobrara river. The surface of the 
country is covered with a superficial deposit of loose sand, which is blown by the wind into 
large conical hills rendering travelling quite difficult. Numerous freshwater and saline 
lakes are scattered about among these sandhills, affording a resort for myriads of water 
birds, ducks, geese, gulls, &c. 
August 10th. On reaching the Niobrara we observed some of the Upper Miocene beds 
exposed in the channel of the river, very rarely, however, containing any organic remains. 
The more recent upper strata (Pliocene), reveal large quantities of the teeth and bones of 
mammals, with fragments of a species of turtle (Zestwdo Niobrarensis, Leidy). 
Section of beds in descending order: 
Alluvial and drift. 
Quite hard arenaceous limestone ; the same rock seen on the Loup fork containing cherry-stones. 15 feet. 
Dark gray friable coarse sandstone. 4 feet. 
Like bed 3, but more heavy-bedded and less distinctly stratified. 30 feet. 
eS eee 
We seem to have represented here the highest bed of the Miocene Tertiary, with a 
full series of the Pliocene. A butte near our camp affording a fine section of the strata, 
measured from the edge of the river with a pocket level, proved to be one hundred and 
sixty-six feet in height. It is composed mostly of a gray calcareous grit, more or less 
compact, sometimes quite incoherent, containing many seams of concretionary sandstone. 
On the summit is a stratum formed of loose layers of limestone, similar to that which con- 
