OF THE UPPER MISSOURI. 35 
off from the granitic nucleus by the upheaval, is a series of azoic stratified rocks, with 
here and there dikes of trap or basalt. These stratified beds consist of gneiss, hornblende, 
Fig. 9. 
= SAO, . Cy Ty AIPA RADE MG wy ne = 
“AO a DOO SK ARNT 
Vee rv \ —— 
area iz SN Nt 
WINN an rany . ZNSE “tt 
PAN yg, SNE NZ 
tii 
oD TARR ec — Nez 
: = if PCAN AI Su = SIMRAN EI Ras MAP RA WW WN 
ont i TENS EG et Aleutian 
micaceous and talcose slates, syenite and white quartz, with other varieties of igneous 
rocks. North of Laramie peak, the Platte river cuts through a large thickness of strata, 
the lower portion of which is composed of metamorphic rocks, the middle a quartzose 
limestone resting unconformably upon the rocks below, and the upper 200 feet or more 
formed of beds of limestone charged with Carboniferous fossils ; but along the eastern and 
southeastern base of the Laramie range the recent Tertiary beds and drift jut up against 
the foot of the mountains, concealing all the fossiliferous rocks. On the south side of the 
Platte I observed the Carboniferous beds in but two localities, Warm spring and Cotton- 
wood creek, where they are exposed at each locality over an area of not more than five or 
six hundred yards square. Proceeding northward from Fort Laramie we meet with fre- 
quent elevations revealing a nucleus of igneous rocks, while on the sides and summits are 
beds of Carboniferous limestone. The highest peak in this direction, forming the eastern 
limit of the Laramie group, is Rawhide peak, which is 800 feet high, and has a similar 
geological and mineralogical structure to Laramie peak and Black hills. No Carboniferous 
rocks were seen immediately in contact with Rawhide peak. Continuing our course to- 
ward the Black hills the indication of the internal forces which elevated the Laramie range 
seem to die out, only comparatively feeble traces remaining to show that the uplift of the 
two mountain groups were connected and synchronous. After leaving the Niobrara no 
rocks older than the Cretaceous formation No. 1 are seen until we reach the Black hills, 
