ransome] COPPER DEPOSITS OE BISBEE, ARIZ. 151 
The dikes are well shown along the southwest face of the main ridge 
west of Bisbee. The larger intrusions are exemplified by the granitic 
mass of Juniper Flat, which is inclosed in schists, and of the smaller 
body of mineralized and altered porphyry forming Sacramento Hill, 
just southeast of Bisbee, and intrusive into schists and limestone. 
The latter mass is of particular significance from its connection with 
the principal copper deposits of the district. The intrusion of the 
porphyry was accompanied by little or no contact metamorphism even 
in the limestones. 
After the intrusion of the granite-porphyry the region was eroded 
until the opening of Cretaceous time. It is probable that the princi- 
pal mineralization of the district followed closely the eruption of the 
porphyry, and thus dates from early Mesozoic time. 
At the beginning of the Cretaceous the region again began to sub- 
side, and a conglomerate was deposited by the advancing sea over the 
eroded surface of the pre-Cambrian and Paleozoic rocks, with their 
intruded masses of porplryry. In places this conglomerate was laid 
down to a uniform thickness of about 75 feet over an even surface, 
but elsewhere it is found filling hollows in a pre-Cretaceous hilly 
topography, and attains a local thickness of 500 feet. The pebbles 
are composed chiefly of schists, although those of limestone and gran- 
ite-porphyry are not entirely absent. With the continued subsid- 
ence of the region about 1,800 feet of unfossiliferous sandstones and 
shales, with occasional lenses of sandy limestone, accumulated above 
the basal conglomerate. Conformably overlying these are about 650 
feet of limestone beds containing abundant fossils belonging in the 
Comanche division of the Cretaceous. Most of these limestones, par- 
ticular! }' the lower beds, are thin bedded and impure, but hard, gray, 
massive beds, aggregating some 40 feet in thickness, occur near the 
middle of the calcareous member of the local Cretaceous section, and 
form a cliff that is a conspicuous topographic feature of the hills 
north and east of Bisbee. The limestones are conformably over- 
lain by more than 2,000 feet of sandstones and shales, much like 
those occurring in the lower part of the section. These upper arena- 
ceous beds are the youngest stratified rocks exposed in the Bisbee 
quadrangle. As their upper surface is everywhere one of erosion, 
their original thickness is unknown. The foregoing Cretaceous strata 
were first described by Dumble, and by him called the " Bisbee 
beds." a 
The Cretaceous beds of the Bisbee quadrangle have been deformed 
by folding and faulting. The folds are generally open, dips of more 
than 20° being rather exceptional. The general strike is northwest 
and southeast, and the prevailing dip northeast. About 7 miles 
southeast of Bisbee, however, where Paleozoic beds have been thrust 
by faulting over the Cretaceous, the latter have been turned up 
a Trans. Am. Inst. Min. Eng., Vol. XXXI, 1902, pp. 703-706. 
