of the Rocky Mountains. : 69 
of the Shyenne river, the most important stream in this region. 
The north branch passes along the north side of the range, re- 
ceiving most of its waters from it, but taking its rise far to the 
westward near the sources of Powder river, in the ‘divide’ be- 
tween the waters of the Yellow Stone and those of the Missouri. 
The south branch also rises in the same ‘divide,’ flows along the 
southern base of this range, receiving the waters of numerous 
tributaries which have their sources in it. 
gain, by referring to the map above alluded to, we ascertain 
that the Black Hills form the most eastern outlier of the great 
ocky Mountain range as well as the first point where rocks 
older than the Carboniferous are exposed to the eye after leav- 
ing the Missouri westward. These Hills would seem to consti- 
changed rocks beneath. The pebbles vary in size from an 
eighth of an inch to four inches in diameter cemented together 
with a silicious paste. Some of the pebbles are scarcely worn, 
While others are quite smooth. At the locality where the fol- 
Owing section was taken, the sandstone is of a gray color tinged 
with red at the base, but ascending it becomes more ferruginous 
Until its color is a dark dull red, and its texture, a coarse grained 
boniferous rocks and the Potsdam sandstone conforming to each 
other, but the latter resting discordantly upon the Azoic stratified 
@ granitic rocks, 
1. A hard, compact fine grained yellowish limestone of an ex- 
cellent quality ine aor into a yellow calcareous sand- 
Stone, quite friable. Fossils: Spirifer tana, Marcou, 
an = - 
yris, like A, subtilita, Cytoceras, &e. - 50 ft. 
