276 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Carboniferous limestones on the southern side showing no marked 
deformation except a sharp backward bend at the porphyry con- 
tact, while on the northern side the whole Paleozoic series from the 
lower beds of the Cambrian to the Upper Carboniferous inclusive 
are upturned at a high angle, overlie the porphyry, and are locally 
faulted. = © = 
“Topographically, Whitewood Canyon laccolith is inconspicuous. 
The traveller on the Fremont Railroad in Whitewood Canyon below 
Deadwood would not suspect its presence. In going down the canyon 
the most striking features seen are the brown Cambrian and white 
limestone cliffs that rise vertically 600 to 700 feet above the bed of the 
muddy torrent. At the bridge the line of the railway crosses the south- 
ern fault, marked in the cliffs by an abrupt transition from limestone 
on the south to steep walls of brown Cambrian flags, limestone breccias, 
and shales, which at the fault are indurated to a gray and black horny 
rock of chalcedonic aspect. ‘Three-quarters of a mile below, a gulch 
is seen on the east side of the canyon that has been eroded out on the 
fault or conduit side of the laccolith. Curious revetting scarps of 
porphyry that at first sight resemble sediments curve up over the spur 
on the north side of the small gulch, while on the south side porphyry 
forms the lower portion of the slope, and above it the contact with 
dragged limestones forms a small bench. ‘The summit of the por- 
phyry hill on the north side is Cambrian Obolus sandstone, containing 
a small sill, that outcrops in a ring about the crest. More conspicuous 
than this summit are the monoclinal ridges of Paleozoic limestone 
north and northeast, the second being Whitewood Peak [Plate 2, fig. 1 
this Bulletin]; at one place the broad yellow bench of Ordovician 
spotted limestone shows a bare rock face with small faults displacing 
the beds. This escarpment is a conspicuous landmark from the sum- 
mits about, and may be seen dipping off the eruptive from the bend of 
Whitewood Creek, where, at a sharp elbow of stream capture, the rail- 
way leaves the canyon by a tunnel through the Minnelusa ridge. 
[Plate 2, fig. 2, this Bulletin.) The Whitewood Canyon laccolith 
differs from the Judith Mountains type of unsymmetrical laccolith 
mountain, Black Butte, in that erosion, by monoclinal shifting, has not 
progressed far enough to give the porphyry relief above the limestones 
which encompass it.” * * * 
“Crook Mountain, adjacent to Whitewood laccolith on the north- 
[east] and separated from it by the synclinal valley of Sandy Creek, 
is the type of a laccolithie dome in which as yet the porphyry core 
has not been revealed by erosion.” 
