ltndgren] COPPER DEPOSITS AT CLIFTON, ARIZ. 135 
being the flat-topped mass of Coronado Mountain. The town of Met- 
calf is situated on Chase Creek, 6 miles north-northwest of Clifton, 
while Morenei is 4 miles distant in a northwesterly direction from 
the same place, but located high up in the hills, 1,000 feet above 
Chase Creek. 
GEOLOGICAL FEATURES. 
The old Pleistocene gravel plateau extending northward from Gila 
River to near Clifton and Morenei has already been mentioned. The 
older rocks rising above this plateau are to a very large extent of vol- 
canic origin and of Tertiary age. The whole region north of the Gila 
River for a distance of at least 100 miles, and probably much more, 
is covered with very heavy flows of basalt and rhyolite. It is, in fact, 
the southern edge of the great volcanic plateau of eastern Arizona. 
Near Clifton original high elevation and extensive subsequent ero- 
sion have combined in forming an exposure of pre-Tertiary rocks con- 
sisting of granite, porphyry, quartzite, and limestone. The Clifton 
area of older rocks may be considered as a small isolated mass, per- 
haps 12 miles long from east to west and 8 miles broad from north to 
south, appearing like an island in the surrounding vast lava flows. 
The oldest rock and that which occupies the largest area is granite, 
evidently of pre-Cambrian age. It forms the great mass of Coronado 
Mountain and the larger part of the precipitous complex of mountains 
between Chase Creek and San Francisco River. 
On the somewhat irregular surface of this granite rests a sedimen- 
tary series of Paleozoic age, the lower part consisting of 200 feet of 
quartzite. Immediately overlying the granite is coarse quartzite con- 
glomerate, in places reaching a thickness of 50 feet. This quartzite, 
in which no fossils have been found, is probably of Cambrian age. 
The quartzite is covered by 800 feet of limestone, the lower part of 
which belongs to the Silurian system, the middle part to the Devonian, 
and the upper hundred feet to the Lower Carboniferous series. 
Beginning from the base, the limestones gradually become purer, and 
the top stratum, well exposed at Morenei, is almost entirely pure car- 
bonate of lime. Within the Devonian portion about 100 feet of clay 
shale is intercalated in the limestones. 
A large mass of porpl^ry, running out at various points into com- 
plicated dike systems, has been intruded into these rocks, granites as 
well as quartzites and limestones, and this porphyry seems most inti- 
mately connected with the origin of the ore. Its character varies 
somewhat. The prevailing rock near Morenei is intermediate between 
a granite-porphyry and a diorite-porphyry, but at some points diorite- 
porphyries of typical character also occur. The porphyry at Metcalf 
is more acidic and contains large quartz crystals. It may more closely 
approach a granite-porphyry, but is, geologically, probabty the same 
body as the Morenei porphyry. 
