36 ISRAEL ©. RUSSELL 
The Cretaceous sandstone surrounding the base of these 
‘buttes is the youngest of the stratified rocks which come in 
immediate contact with the igneous intrusions we are studying, 
and presuming that all the igneous rocks are of the same date, 
records the upper limit as nearly as can be determined, to be 
placed on estimates of the time of their origin. That is, they are 
younger than the Middle Cretaceous. 
Inyan Kara.—This lone butte stands in Wyoming on the west 
side of the main uplift of the Black Hills. It has not been seen 
by the present writer except from a distance but has been described 
by both Winchell and Newton. As Newton’s visit was the more 
recent we quote his description almost entire :* 
Its name first appeared on a map published by Lieut. Warren 
in 1858, and as translated for him, signifies ‘‘the peak which 
makes stone.” Its summit is 6600 feet above the sea, and has 
an elevation of 1300 feet above the bed of the Inyan Kara Creek 
near by. The igneous mass of the peak occupies the center of 
what in form resembles a crater, for separated from it by an 
annular valley there is an encircling ridge or rim whose top is 
500 feet below the summit of the peak. This rim is formed of 
Red Bed limestone rising up from under the surrounding red 
clays at an angle of about 40° and completely encircling the 
peak except at a narrow break on the northeast side where the 
drainage escapes. The limestone wraps around the outer slope 
of the peak like a cloak, conforming to all local changes of dip 
and is without fracture. The upper red clays of the Red Beds 
lay up against this limestone, and in conformity with it dip away 
in all directions. On the inside of the rim is the annular valley, 
surrounding the igneous nucleus and having a width, from rim 
to center of peak, of from one-half to three-fourths of a mile. 
It has evidently been formed by the denudation of the easily 
eroded strata beneath the limestone. 
From the midst of the crater-like depression the peak rises 
so abruptly that there is but one side with an easy slope for 
climbing. The summit is a broad but very irregular area, whose 
* Geology of the Black Hills, pp. 197-199. 
