Geology of Lincoln Co.. S. D. — Bcndrat 73 
A\'hile the Benton is found exposed only about 20-30 feet, 
well-boring- has revealed its real thickness for instance at 
Worthing, near the axis of the trough 203 feet, and in T.99N., 
R.51W.. X.W. of Lennox, 94 feet. 
c : The Niobrara Chalkstone. 
The chalky series of the Niobrara has been identified be- 
yond doubt along Beaver creek. Long creek, the bluffs of the 
Big Sioux, Pattee and E. and W. Brule creeks. 
One mile north of Worthing and two miles east of that 
town, witiiin sec. 34 of La \'alley township, it has been found 
exposed in the northern bank of Beaver creek for about 2-4 
feet, while the rest of it was hidden by talus. It showed traces 
of fossils, which, however, were too fragmentary to allow of 
identification. Within the seventh mile east of Worthing, in 
the eastern bank of Beaver creek, a very fine exposure of about 
10-15 feet of the chalky series was met with, comparatively 
rich in fossils. The most of them were "Ostrea congesta" 
Conrad, identified through the kindness of Dr. T. W. Stanton, 
paleontologist of the U. S. Geological Survey, and a large 'Tn- 
oceramus" species, of which, however, only fragments could 
be found. The top of the exposure was found to be about 
1320 feet above sea level. 
Farther southeast, where the southern bank of the Big 
Sioux rises in high bluffs above the stream, west of Fairview, 
the chalky series has been found at practically the same level, 
i.e. about 105 feet above the stream. Within T.98X., R.48W., 
23^ miles west of Fairview, it is exposed for about five feet in 
cuts at both sides of the road leading down the slope of the 
terrace to the bottom-land of the Sioux, the top of the form- 
ation being nearly 100 feet above the level of the stream. 
In the southern part of the region the Xiobrara is again met 
within the valleys of Pattee creek and East and West Brule 
creeks, in the latter exposed in places for about 30 feet. The 
bottom of the valley of the western fork of West Brule creek 
was found to consist of calcareous clays, while about 10 feet 
above the level of West Brule creek the chalky series was met 
with again, directly imderlain by the Benton. 
As to the thickness of the formation no absolute data were 
available from well-borers, who apparently take the chalkstone 
for a similarly looking deposit above or beneath the level of 
