50 LARAMIE BASIN, WYOMING. 
Montana. Northwest of Centennial the sedimentary rocks disappear 
beneath the glacial debris of North Fork, but the granite crosses the 
strike of beds from Casper to Montana on a fault which joins the 
Sheep Mountain fault. 
SHEEP MOUNTAIN TO ARLINGTON. 
The contact of the sedimentary rocks and the granites northward 
from a point 2 miles north of Woods Landing is very irregular owing 
to a cross fault associated with irregular flexing. At this point the 
Chugwater beds dip toward the schists at an angle of 12° near the 
contact. The south end of Sheep Mountain is marked by an escarp- 
ment which corresponds to the junction of the schists with the granite 
that constitutes most of Sheep Mountain. The granite at the east 
face of this mountain rises about 250 to 300 feet higher than the 
schists immediately south, and farther west the granite is 800 feet 
higher than the Tertiary deposits which lie upon the old level eroded 
surface of the schists. The top of Sheep Mountain shows another 
such level eroded surface, apparently once continuous with the sur- 
face just mentioned, and now uplifted by the dislocation. The schist 
mass appears to have been rotated on an axis lying near the east face 
of the mountain, for along the apparent continuation of the fault on 
the plains to the east the Morrison is in contact with the Niobrara, 
indicating downthrow on the north side, whereas west of the axis of 
rotation the downthrow is to the south. To the west this fault 
probably cuts off the beds in the south end of the Centennial Valley 
and passes into the Medicine Bow Mountains. In the valley the 
upthrow is on the south side. 
For a mile along the east base of Sheep Mountain north of this cross 
fault a long slope of debris entirely obscures the contact, but farther 
north there are a few outcrops of Chugwater and Niobrara, the former 
beds lying higher in the slope than the latter and both dipping toward 
the mountain at an angle of 70°. A great fault begins in this vicinity 
and extends northward beyond Arlington. West of Lake Flattie 
this fault brings the upper beds of the Montana,- dipping gently to the 
west, into contact with the granite, as shown in section 4, Plate VIII. 
The granite rises in a steep slope to the crest of Sheep Mountain, 
1,500 feet above. The amount of throw diminishes toward the 
north as the Sheep Mountain anticline pitches down, and is small in 
crossing the syncline of the Centennial Valley east of Centennial. 
Farther north the fault reaches the flank of the uplift of the Medicine 
Bow Mountains, and granites and the Montana are again in contact. 
This relation extends beyond Rock Creek except in a ridge south of 
Arlington, where some red beds (presumably Chugwater, probably 
lying on Casper formation) appear for a short distance along the west 
