138 KANSAS ACADEMY OF SCIENCE. 
extend for a number of miles up the Big Sioux river. AtSioux City an exposure 
may be seen at Prospect hill, a bold bluff on the bank of the Missouri. 
From this place the river crosses the broad valley and strikes the bluffs on 
the west side at the old mission, some twenty miles below. On the east side the 
bluffs trend to the southeast. A shoulder standing boldly out toward the river 
has received the name Sergeant’s bluff, in honor of Sergeant Floyd, a member 
of Lewis and Clarke’s party, who was buried on its summit. It is on the face of 
this bluff that the Dakota clay, which is very similar to that at Sioux City, is 
being excavated for brick and tile. The exposure is a quarter of a mile long, and 
the total thickness of the beds is said to exceed fifty feet. A considerable por- 
tion, however, consists of sandstone arranged in lenses and pockets; and near 
the top is a rather heavy sandstone ledge. Numerous leaves are found in some 
reddish-brown concretions scattered throughout the shales. 
For maps showing the exposures of the Dakota in Kansas and Nebraska, 
reference is made to the University Geological Survey of Kansas, vol. II, pl. 
xvi, for the Kansas areas, and to the Nineteenth Annual Report of the United 
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