Logan. | The Upper Cretaceous. 223 
being occupied by the lower Benton shale. North of Minersville, 
on West creek, the overlying shales of limestone have been removed 
by erosion, leaving the saliferous shales exposed. The latter, by 
weathering, have formed a salt marsh of several hundred acres in 
extent. An upward pressure of the water in the underlying Dakota 
strata has caused, in many parts of the marsh, the shales to assume 
the character of muck. <A well was bored in this marsh to a depth 
of 150 feet. The water, owing to a local dip of the underlying strata, 
rose above the surface to a height of 12 feet. A salt marsh twelve 
hundred acres in extent occupies the same horizon on Buffalo creek, 
northwest of Jamestown. 
Benton.—In passing up the valley from Concordia to Jamestown, 
the last Dakota outcrop toward the southwest occurs a mile east of 
Jamestown. But farther toward the west, on Buffalo creek, out- 
crops of Dakota sandstone are of frequent occurrence. The surface 
of the country from Jamestown to Scottsville rises gradually, pass- 
ing through the lower Benton formation. The Benton limestone 
is found everywhere capping the hills south of Jamestown, but dis- 
appears under a gradually thickening bed of the Ostrea shales as 
Scottsville is neared. AIl of the horizons of the Benton limestone 
are marked, but the Lincoln marble is less distinctly marked here 
than elsewhere, and in some outcrops seems to be wanting alto- 
gether. One outcrop shows seven layers of limestone varying in 
thickness from 2 to 9 inches, and intercalated with yellow rather 
closely textured shales, which contain the Ostrea congesta. From 
Scottsville to Beloit the slope of the country is toward the east and 
south. The Ostrea shales cover the surface, but many of the streams 
have cut down to the lower Benton, or the Upper Dakota. On West 
Asher creek in an exposure of 37 feet, are fourteen layers of Benton 
limestone, intercalated with shales. This limestone disappears 
under the Ostrea shales farther to the north. The limestone layers 
vary in thickness from 2 to 6 inches, and the shale beds from 6 inches 
to 2 feet. The most characteristic fossil of the limestone is the 
Inoceramus liabatus. | 
The Upper Dakota appears on the Solomon river at Beloit in a 
layer of sandstone from 2 to 3 feet in thickness, resting on a bed of 
blue cclored shale. The sandstone strata is very fossiliferous. 
