LoGAN. | The Upper Oretaceous. 229 
THE BENTON SECTION FROM BELOIT TO TIPTON. PLATE XXXI, 
FIGURE 1. 
Starting at Beloit and passing to the southwest a distance of 
twenty tive miles, we cross the exposed surface of each of the 
Benton divisions. The altitude of the Upper Dakota stratum at 
Beloit is 1350 feet, and the altitude of the highest Benton stratum 
on the Blue Hills is 1850 feet, making a difference in altitude, for the 
twenty five miles, of 500 feet. About 50 feet above the Upper 
Dakota horizon appears. : 
The Benton Limestone Group.—The Benton limestone group here 
consists of layers of compact white limestone, intercalated with 
bands of yellow shale. On the bluffs south of Beloit the Benton 
limestone appears and disappears a few miles back under the Ostrea 
shale. The surface soil rests upon the Ostrea shales from this point 
to the base of the Blue Hills. 
The Ostrea Shales.—The Ostrea shales underlie the surface soil 
of the greater part of Mitchell, Jewell, Cloud, Lincoln and Russell 
counties. The upland areas of these counties have almost as fertile 
a soil as the bottom lands, a condition due largely to the Ostrea 
shales. 
ithe Blue Hill Shales.—Near the base of the Blue Hills we find the 
lower horizon of the Blue Hill shale, and at the top the upper hori- 
zon containing the Septaria. A rather heavy deposit of Ft. Hays 
limestone rests upon the shales and prevents their erosion. The 
shales here do not differ from those found in other localities. 
THE FORT PIERRE SHCTION FROM ST. FRANCIS TO THE ARICKA- 
REE RIVER. PLATH XXXII, FIGURE 1. 
At St. francis the Fort Pierre shales are very near the surface. 
St. Francis is located in the valley of the south fork of the Republi- 
can, which has cut down into the Tertiary a distance of from 150 to 
200 feet. The surface of the Fort Pierre bed is very uneven at this 
point as indicated by the records of the wells. One well pierced the 
shale at 8 feet without reaching water, but another one only a few 
feet to the west, passed through 16 feet of sand and gravel without 
striking shale, and found abundance of water. Another well was 
dug, one half passing through shale the other half through sand. 
