IGNEOUS INTRUSIONS IN THE BLACK HILLS 43 
in a contour map by Newton and Gilbert,’ it would now form a 
great, elongated dome, about 80 by 160 miles in diameter, and 
rising 7000 feet above the encircling plain. The central core of 
this vast dome is composed of schist and granite, from which 
the surrounding sedimentary beds dip away in all directions in 
the same manner as they do about the Sun Dance hills. 
Great as is the Black Hills dome, it is far surpassed in size 
by a similar uplift forming the Big Horn Mountains, rising some 
180 miles to the westward, and by several of the ranges in the 
Park Mountains, Colorado. 
Some of the thoughts suggested by these and other compari- 
sons, with reference to the origin of great domes in a broad region 
of horizontal rocks, will be presented in a future paper in this 
JOURNAL. 
ISRABL IC. KUSSELL: 
t Geology of the Black Hills, Pl. cf p. 208. 
