150 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
nail} 7 shales or arkose sandstones which were folded and metamor- 
phosed into their present crystalline condition before Cambrian time. 
After long erosion these schists were reduced to a surface of very 
slight relief, which in Cambrian time was submerged beneath the sea 
and covered with the sands that are now represented by quartzite, 
from 400 to 500 feet in thickness. The submergence of the area con- 
tinued, and about 750 feet of thin-bedded, cherty, fossiliferous Cam- 
brian limestones accumulated on top of the quartzite. No record of 
Silurian time has been discovered in the Bisbee quadrangle. Over- 
lying the Cambrian limestone, apparently in perfect conformity, are 
340 feet of dark-colored, compact, rather thin-bedded limestones, with 
some intercalated shales, all carrying an abundant and characteristic 
Devonian fauna, consisting chiefly of brachiopods and corals. 
The opening of Carboniferous time was, in this region, unmarked 
by any interruption of the continued subsidence. No unconformity 
has been detected between the Devonian and the Lower Carbonifer- 
ous (Mississippian) rocks. The latter consist of white or light-gray 
granular limestones, often made up almost entirely of crinoid stems 
and containing a fairly abundant brachiopod and coral fauna. The 
thickness of the Lower Carboniferous limestone may be provisionally 
given as 700 feet. The beds are often 6 feet or more in thickness and 
commonly form cliffs overlooking slopes carved from the less resistant 
Devonian and Cambrian limestones. 
There is in the Mule Mountains no discoverable stratigraphic break 
between the Lower and Upper Carboniferous beds. Subsidence appar- 
ently continued, and the generally thinner beds of Upper Carbonifer- 
ous (Pennsylvanian) limestone accumulated to a thickness of over 
3,000 feet above the Lower Carboniferous. The Upper Carboniferous 
limestones are usually more compact in texture than those of the 
Lower Carboniferous, and are more fossiliferous. They are also some- 
what more variable in color, pinkish and yellowish beds being of fre- 
quent occurrence. 
The local Paleozoic section from the pre-Cambrian schists very 
nearly to the top of the Lower Carboniferous is well exposed on the 
northeast face of the main ridge about 1J miles west of Bisbee. The 
Upper Carboniferous beds are best seen in the hills just north of Naco 
Junction (5 miles southwest of Bisbee), and the relation between the 
lower and upper divisions is well shown near the Whitetail mine, 
about 2 miles due south of Bisbee. 
At some time during the interval between the close of the Carbon- 
iferous and the opening of the Cretaceous the long-continued subsi- 
dence and sedimentation of the region were interrupted by extensive 
faulting, probably connected with uplift. Accompanying or immedi- 
ately following the faulting came intrusions of granitic magma which 
solidified as granite, granite-porphyry, and rhyolite-porphyry. These 
intrusions took the form of dikes following fault fissures, of sills 
injected between sedimentary beds, and of irregular stock-like masses. 
