Per cent

Silicia 13 . 7

Alumina 5.3

Ferric iron 2.4

Calcium carbonate 64 . 2

Magnesia 0.7

Sulphur trioxide 0.7

Caiionaceous material 8 . C

This is the southermost natural exposure of the Niobrara
region. Half a mile to the south a well passed through pra(
the same succession of layers and seven or eight miles furthe
or about four miles west of Edinburg a deep well struck tl
brara after passing through 150 feet of Pierre shale.
Xo. 3 and succeeding yellow layers consist of a very f
yellowish clay. It is very soft and free from grit, stron
sembling cheese in its texture. Unlike most clay howev<
absolutely devoid of plasticity, crumbling down into an i
ent mass when moistened. When unweathered it is dark
but on exposure to air turns very quickly to a yellow colo:
ably on account of the rapid oxidizing of the ferrous salt;
in contains. It tastes strongly of alum and analysis re



CEMENT MATERIALS



The workings of the cement company reveal very well I
acter of the cement rock at this place. One tunnel extend
nine hundred feet into the face of the bluff and discloses t
faults or slips whose strike is approximately north. They {
angle of about seventy-five degrees from the horizontal, I
ping west. They have finely developed fault planes and
face where the slip has occurred is very smooth and
These displacements show that at one time or another tl
been some slight disturbance, perhaps a slight folding w
sequent faulting.
