228 University of Kansas Geological Survey. 
Russell counties. The Benton area may be recognized by the stone 
fence posts which are used in these localities. These fence posts 
are taken from the Fence-post horizon of the Benton group. The 
majority of the houses in this area are built of the Benton limestone. 
The Ostrea Shales——The Benton limestone is superseded by the 
Ostrea shales. These shales contain here, as elsewhere, the charac- 
teristic Ostrea congesta, and gypsum veins. Many outcrops occur 
along the river west of Mungor, and the surface of the country lies 
within the Ostrea horizon. 
The Blue Hill Shale—The Blue Hill shales which overlie the 
Ostrea shales occur in banks along the river from White Rock to 
the mouth of the Hackberry. They everywhere underlie a bed of 
Ft. Hays limestone. At Cedar Bluff, a 50 foot bed of Blue Hill 
shales is overlaid by a'30 foot bed of Fort Hays limestone. At the 
mouth of the Hackberry a 45 foot ledge ‘of Ft. Hays limestone 
rests upon a bed of Blue Hill shales in which the Septaria concre- 
tions are embedded. The Septaria marks the dividing line between 
the Benton and Niobrara. Passing up the Hackberry ‘we find the 
Kt. Hays limestone overlaid with chalk cliffs, varying from a few 
feet to 100 feet in thickness. 
The Niobrara.—These chalk beds with the underlying Fort Hays 
limestone belong to the Niobrara formation. The outcrops of the 
chalk, or Pteranodon beds are almost continuous from a few miles 
above the mouth of the Hackberry to the western line of the state. 
The famous Castle Rock, see Plate VII, a single chalk mound 
70 feet high, is located on the Hackberry about seven miles from its 
mouth. Tbe Pteranodon beds occupy the country along the Smoky 
Hill river a distance of from one to three miles on each side from near 
the mouth of the Hackberry to Russell Springs. The hills back from 
the river are covered with the Tertiary formation. From Russell 
Springs to the state line the outcrops occur only at the river’s ° 
banks and become less and less frequent as the line is neared. 
