LoGaN. | The Upper Cretaceous. BAT 
problematicus, and resembles a mortar bed into which. shells have 
been thrown. The Inocerami casts are well preserved, and, although 
found throughout the upper limestone group, are most abundant 
in this horizon. For this reason the name Inoceramus has been 
given to the horizon. The shell rock, or lime rock as it is called 
locally, is used to a limited degree in the manufacture of lime. 
The Fence-Post Horizon.—Near the top of the limestone group is 
the Fence-post horizon, so named because the limestone is used very 
extensively for making fence-posts. It is estimated that there are 
at least fifty thousand of these posts in use in Mitchell and Lincoln 
counties alone, five thousand being used in a single township. Their 
use is becoming general throughout the Benton area. The average 
thickness of the fence-post limestone is 9 inches. A ferruginous 
seam passes through the center of the layer and by splitting the 
limestone along this seam excellent flag-stones are produced. 
The fossils found in the Mence-post horizon are chiefly invertebrates. 
Species of the genera Aspidorhynchus and Osmeroides have been 
found. With the exception of the Inoceramus group the limestone 
from each of the horizons is used for building purposes. . 
THE UPPER GROUP. 
The upper group contains two horizons, namely, the Ostrea 
shales, and the Blue Hill shales. This group represents a total 
thickness of 250 feet. | 
The Osirea Horizon—The Ostrea shales rest conformably upon 
the fence-post horizon of the lower group. ‘They consist of a bed 
of argillaceous shales of variegated colors, from 100 to 150 feet in 
thickness. The characteristic fossil of this horizon, from which it 
has been named, is the Ostrea Congesta, beds of which occur through- 
cut the horizon. These shells are usually found adhering to the 
bivalve Haploschapa capax. Remains of squaladont selachians and 
sestrationt selachians have also been found. In certain localities 
the shales are somewhat saliferous, forming wherever exposed, salt 
pans or licks. These pans are never of very large area and are 
usually recognized by their whitish appearance. In the extreme 
upper horizon the Tennuicarinata serpula is the chief fossil form. 
It is the disintegrated Ostrea shales that form the soil for the 
