5L.] 
SOUTH DAKOTA. 
297 
aramie, all dipping away from the central nucleus. There are also extensive over- 
ips of the Tertiary deposits, which underlie much of the adjoining plains area, 
he region is one of exceptionally line exposures, which afford rare opportunity for 
Study of stratigraphic relations and variations. Many of the rocks are hard, and 
ie streams flowing out of the central mountain area have cut canyons and gorges, 
t the walls of which the formations are often extensively exhibited. The structure 
resented locally is that of a monocline dipping toward the plains. The oldesl sedi- 
lentary rocks constitute the escarpment facing the crystalline rock area, and each 
igher stratum passes beneath a newer one in regulai succession outward toward the 
largin of the uplift. The sedimentary formations consist of a series of thick sheets 
sandstones, limestones, and shales, all essentially conformable in structure. The 
verlapping areas of the Tertiary deposits extend across the edges of the older forma- 
ons. The stratigraphy presents many features of similarity to the succession of 
>cks in the Rocky Mountains of Colorado and Wyoming, but it possesses numerous 
tstinctive local features. 
The following is a list of the formations which are exhibited in the uplift, with a 
laeralized statement as to the thickness, characteristics, and age: 
Generalized section in the Black Hills region. 
Formation. 
Character. 
A verage 
thickness. 
Age. 
Feet. 
Laramie 
Massive sandstone and 
shale. 
2,500 
Cretaceous. 
Fox Hills 
Sandstone and shale 
Dark-grav shale 
250-500 
1,200 
Do. 
Do. 
Pierre shale 
Niobrara 
Chalk and calcareous 
shale. 
225 
Do. 
Benton group: 
Carlile formation 
Gray shales with thin 
sandstones, lime- 
stones, and concre- 
tionary layers. 
500-750 
Do. 
Greenhorn limestone 
I mpureslabby limestone 
50 
Do. 
Graneros shale 
Dark shale with lenses 
of massive sandstone 
in its low r er part at 
some places. 
000 
Do. 
Dakota sandstone 
Massive buff saaidstone. . 
35-150 
Do. 
Fuson 
Very fine-grained sand- 
stone and massive 
shales. White to pur- 
ple color. 
30-100 
Do. 
Minne waste limestone . 
Gray limestone 
0-30 
Do. 
Lakota 
Massive buff sandstone, 
with some interca- 
lated shale. 
200-350 
Do. 
Beulah shale 
Pale grayish-green shale. 
0-150 
Jurassic. 
Unkpapa sandstone . . . 
Massive sa n d stone ; 
white, purple, re d , 
huff. 
0-250 
Do. 
