The different layers of cement rock vary widely in i
tion. They may show the following or even greater r

chemical composition :

Per a

; Calcium carbonate 35

Silicon dioxide 12

Ferric oxide 3

Aluminum trioxide 4

Magnesium carbonate

Sulphur trioxide 0.25-0

A remarkably uniform and fine-grained layer, at preset
used for the manufacture of cement, has the following c

tion:

Per c(

Calcium carbonate 0-*

Silicon dioxide 14

Alumina and ferric oxide 7

Magnesium carbonate , tr

Sulphur trioxide

This material when properly burned and ground makes
which in comparison with the average Portland brands lea
little to be desired. The material is easily mined, it break:
clean roof and floor, and requires comparatively little timb

Outcrop in the southeast quarter of section 11, T. 161, '.
Feet.
7. Unexposed to top of bluff

6. Shale 6

0. Clay seam yellow

4. Shale, Pierre 10

3. Unexposed 15

2, Clay bands , yellow and black (J

1. Shale, calcareous, "cement rock" 13

A mile east of the old McLean Post Office, on the sar
as the above exposure, the black and yellow bands are ex
a cut recently made in improving the roadway, on the no



168 CEMENT MATERIALS

of the creek. They are much decomposed but easily recognized
upon examination, and are covered with about five feet of sand and
soil.
Nearly five miles due north of this place, in the Pembina delta
a deep well struck cement rock at a depth of sixty feet. About
six miles south and one mile east of McLean cement rock was
struck at thirty feet. This seems to show that the Niobrara exists
quite generally under the drift and lacustrine deposits of the Red
River Valley at some distance east of the escarpment.
