STRUCTUEE. 47 
slope of Laramie Mountains the strata descend in regular order, and 
in the center of the basin west of Cooper Lake the base of the sedi- 
mentary series is several thousand feet below the surface, as shown 
in section 3, Plate VIII. At the south end of the basin there is a 
general upward pitch of the strata; to the north the basin is crossed 
by a series of extensive corrugations, shown in section 2, Plate VIII. 
The monocline of the Laramie Mountain slope is cut by a fault near 
Tie Siding. This fault, so far as it is marked by the contact of sedi- 
mentary rocks with the granite, has a length of about 3 miles, extend- 
ing north of west from a point near the middle of the north side of 
sec. 33, T. 13 N., R. 72 W., nearly to the middle of the north side of 
sec. 25, T. 13 N., R. 73 W. It probably extends some distance beyond 
the end of the contact of the sedimentary rocks and the granite. 
The sedimentary rocks dip toward the fault at a low angle. No 
accurate measurement of the throw is possible, but as the dip of the 
strata is toward the fault plane the throw can not be less than the 
difference of elevation between the beds on the ridge and those in 
the hollow to the north, which is 250 feet. The throw is therefore 
between 250 and 500 feet. The hade is very steep but the fault plane 
was not seen, and whether the fault is normal or reverse is not known. 
A small fault traverses the Casper formation east and northeast of 
Pilot Knob, on the axis of the small anticline that crosses the moun- 
tain slope east of Howell. On Horse Creek this fault has an upthrow 
of about 200 feet on the east side. 
BOULDER RIDGE ANTICLINE. 
In the southern portion of the Laramie Basin the main synch ne is 
divided into two lobes by a prominent anticline extending from the 
south and finally pitching down to the north. One of its most 
marked features is Boulder Ridge, a rugged prominence of granite 
which extends for some distance northward along the axis of the 
uplift. The flexure is conspicuous in the formations from Chugwater 
to Benton south of Hutton Lake and in the Niobrara formation in 
the west end of The Big Hollow, and its effects are clearly marked 
by uplift in the Montana beds for some distance farther north. 
In general this anticline presents very steep dips on the east side 
and gentle dips on the west. From the north end of Boulder 
Ridge to the south line of T. 13 N. the east side of the anticline is 
faulted. This is indicated by the facts that the contacl line between 
the granite and the Casper formation is nearly straight, and that as 
the various limestone and sandstone beds swing in to the west they 
are abruptly cut off by the granite, which here rises in a steep front 
300 to 500 feet high. South of the township line the eastern slope 
of Boulder Ridge is less abrupt and the sedimentary rocks, which 
dip to the east at steep angles, extend for some distance up the Hank 
