OF THE UPPER MISSOURI. 17 
the same rocks exposed in outcropping narrow belts, sometimes expanding so as to occupy 
a wide area; again concealed or eroded away so that scarcely a trace can be seen. The 
plain country is occupied by the upper members of the White river Tertiary. The nucleus 
of the mountains is composed of granitoid rocks with very little variety. I shall dwell 
more at length on the general geology of this region in a succeeding chapter. 
In the Laramie range are beautiful valleys with streams of pure water, margined with 
birches, poplars, and other trees such as are met within more northern latitudes. Not un- 
frequently there are broad level plains with a soil composed of the disintegrated materials 
of the granitoid rocks, sustaining a good growth of vegetation. The mountains are 
covered with a fine growth of pine timber, which would furnish an almost inexhaustible 
supply of lumber for economical purposes. 
CPE AG Vee 
FORT LARAMIE TO THE BLACK HILLS. 
About seven miles north of Fort Laramie, we pass the eastern extension of the Laramie 
hills, which is composed of numerous centres of upheaval, by which the granite is pro- 
truded and the overlying rocks thrown off in every direction. ‘The elevations vary from 
one hundred to eight hundred feet in height, the nucleus formed of granitic and azoic 
rocks, while the Carboniferous limestones are scattered over the sides or base of the 
upheaved masses, or lie unconformably upon their summits. The Carboniferous limestones 
incline at various angles, depending upon the power of the disturbing force from beneath, 
and when unchanged by heat contain a few fossils. We can here see every variety of the 
limestone, from the unchanged fossiliferous, to the completely metamorphosed rock, with 
the indications of stratification nearly or quite obliterated. Sometimes the melted ma- 
VOL. XII.—3 
