OF THE UPPER MISSOURI. 25 
as it were. ‘The streams cutting through this bed in various directions have formed deep 
cations with perpendicular sides, rendering travelling quite difficult. 
The valleys in the Black hills are quite pictur- 
esque from the incoherent character of the materials 
of the brick-red bed, which are strewed everywhere. 
On the hills I find the following beds represented : 
1. Gray sandstone. 30 feet. 
2. Yellowish, laminated, argillaceous shale, with numerous fossils. 
Avicula (Monotis) tenurcostata, Lingula brevirostris, Penta- == 
crinus usteriscus, and many specimens of Vermetes, &c. 
20 feet. 
3. Dark bluish ash colored shale, with fossils same as in last bed. 
30 feet. 
4. White sandstone passing down into a red, coarse-grained, heavy-_ 2==— 
bedded sandstune. 50 to 80 feet exposed. 
The sandstone which caps the hills is often broken 
into immense tabular masses, the surfaces of which 
are covered with trails of Planarian worms or mollusks, also impressions of raindrops and 
waved ridges such as are often seen on the shore of a stream. 
We passed to-day over the brick-red bed beneath the blue limestone, both of which are 
fully represented. This lower bed, F, of the vertical section, which is so conspicuous in 
our day’s march, is most variable in its character and color, changing from a nearly white 
to a deep red color, and from a friable grit to a compact silicious rock ; sometimes it be- 
comes a conglomerate composed of nodules and slightly worn fragments of flint rock, 
apparently from the Carboniferous rocks beneath. ight miles before reaching our camp 
of September, we met with the true Carboniferous limestones for the first time, though 
they are everywhere revealed near the central portions of the Black hills. First an | 
arenaceous limestone is seen, then a bluish limestone with cherty nodules like bullets, and 
a few characteristic fossils. The sandstone which we have before mentioned as so variable 
seems to rest conformably on the Carboniferous rocks, though all the beds are more or less 
distorted. When the Carboniferous rocks appear, the country becomes much more rugged 
and uneven, being elevated into high ridges, from the sides of which the different strata of 
limestone project and incline at all angles. 
We remained during the day in the central portion of the Black hills. Here we find 
the Carboniferous rocks and the Potsdam sandstone conforming to each other and resting 
unconformably upon the metamorphic rocks, No rocks more recent than the Carboniferous 
VOL. X1I1.—+ 
