184 USWRAIBIE (Cy IRAUSSIEILIL 
and thinning of the beds over the summit of the dome is to be 
inferred, but thus far has not been observed. 
The Little Sun Dance dome is about a mile in diameter. 
The Inyan Kara dome measures about two miles in diameter. 
The similar dome from which Warren Peak has been sculptured, 
was two or three by eight miles in diameter. The Black Hills 
dome, as shown by Newton and Gilbert, is less regular in ground 
IDEAL Cross-SECTION OF THE BLACK HILLs. 
Vertical scale 5-6 times horizontal. Dotted lines indicate portion of uplift removed 
by erosion. 
1. Archeean slates and schists. 5. Red beds. 
2. Granite. 6. Jura. K 
3. Potsdam unconformably on 1 and 2. 7. Cretaceous. 
4. Carboniferous. 8. White River Tertiary unconformably on 7. 
plan than those just mentioned, and measures 70 by 160 miles in 
diameter. 
The plugs of igneous rock which lead to the elevation of the 
Inyan Kara and several associated domes, have been exposed by 
erosion, and rise boldly in the center of the encircling rings 
formed by the truncation of the domes that formerly arched over 
and concealed them. In the center of the concentric outcrops 
of stratified rocks forming the outskirts of the Black Hills, there 
is a mass of schists into which a core of granitic rock has been 
intruded. The succession of stratified rocks forming the dome, 
and their relation to the schists and granites within, is shown in 
the following section copied from Newton and Gilbert. It is to 
be remembered that any cross section through the Black Hills 
uplift would show the same structure, although the details would 
be varied. 
The schists shown in the central part of the section, belong to 
the series of stratified rock resting on them, so far as the origin 
