18 ON THE GEOLOGY AND NATURAL HISTORY 
terial is thrust up through the seams in the unchanged mass, so that in a single hand 
specimen we have the changed and unchanged rock. Not unfrequently the limestones 
are elevated in such a manner that the strata preserve their horizontality very nearly ; 
again they dip at an angle of from 5° to 30°. 
The above sketch, taken by Lieut. Warren, about six miles north of Fort Laramie, ex- 
hibits some of the phenomena just mentioned. a. Represents metamorphic rocks distorted 
at different angles. 0. Strata of Carboniferous limestone capping the summit of the 
upheaved peak and still retaining their horizontal position. 
Passing from the Platte toward the Niobrara, the upheaved ridges seem to tend in a 
northerly direction, and are for the most part capped with limestones in a more or less 
changed condition. At the foot of these ridges the upper beds of the Tertiary may be 
seen insinuating themselves into the valleys and ravines or deposited high up on the sides 
of the elevations, thus, as it were, filling up to some. extent the inequalities of surface 
formed by the upheaval. In all cases the Tertiary beds are undisturbed and not unfre- 
quently rest directly upon the vertical edges of the azoic stratified or granitic rocks. Raw- 
hide peak is about eight hundred feet high and of the same geological character as Lara- 
mie peak. High upon its sides may be seen remnants of the Tertiary beds, left after 
denudation ; showing very clearly that all these elevations and ridges once formed rocky 
islands in the great Tertiary lake. 
Near Rawhide peak the quartzose limestone appears again in a more or less disturbed 
condition. A section across the vertical edges of the strata would stand thus: 
1. Quartzose limestone with stratification nearly or quite obliterated. 
2. Laminated clay slate. 
3. Alternate strata of Gneiss, Horibleaide, &e. 
Directly west of Rawhide peak we have the greatest thickness of stratified azoic rocks 
met with on the trip. The strata were vertical and I could obtain a section only across 
the upturned edges. : 
Carboniferous limestone. 100 to 300 feet. 
Quartzose arenaceous limestone. 150 feet. 
Soft bluish clay slate. 15 feet. 
Very compact quartzose arenaceous limestone. 500 to 700 feet. 
Steel gray Hornblende. 30 feet. 
A compact crystalline limestone with a somewhat fissile structure which gives it the appearance of being 
laminated, breaking into large rhomboidal masses. 80 to 100 feet. 
Steel gray gneissoid slate with veins of white quartz disseminated through it. 150 feet. 
. Very hard gneissoid rock. 80 to 100 feet. 
rr Pf 
a 
