lindqhkn] COPPER DEPOSITS AT CLIFTON, ARIZ. 137 
material, and the foothills of the mountain complex were buried, up 
to an elevation of 4,500 feet. 
The last phase in the geological history is the present period of 
erosion, which has removed large masses of these early Pleistocene 
gravels and deepened the canyons and gulches to the level which they 
had attained before the volcanic eruptions. 
ORE DEPOSITS. 
Contact-metamorphic deposits. — There is no evidence of ore deposits 
having been formed in this region before the intrusion of porphyry. 
This event appears to be in most intimate connection with the origin 
of all the copper deposits in the region. Wherever the porphyry 
came into contact with the granite or the quartzite, little alteration 
is observed; but wherever we find the porphyry adjoining the lime- 
stones or the shales of the Paleozoic series, very extensive contact 
metamorphism is noted, resulting in the formation of large masses of 
garnet and epidote. This alteration is particularly observable at 
Morenci. The whole Paleozoic series is affected, but more particularly 
the pure limestone of the Lower Carboniferous, which, for a distance 
of several hundred feet from the contact, has been converted into an 
almost solid mass of garnet. The shales have suffered less from this 
metamorphism, but near the porphyry are apt to contain epidote and 
other minerals. This metamorphism appears not only at the contact 
of the main mass of porphyry forming the southern slope of Copper 
Mountain, but also in the hills between Morenci and the Longfellow 
mine, in which dikes have produced contact-metamorphic minerals 
along their sides. Wherever alteration has not masked the phe- 
nomena, magnetite, pyrite, chalcopyrite, and zinc blende accompany 
in various proportions the contact-metamorphic minerals, and are 
intergrown witli them in such a way that the contact-metamorphic 
origin of these ores appears be} T ond doubt. In many places the ores 
have accumulated along certain horizons in the sedimentary series, 
evidently more suitable than others to the processes of alteration 
which produced the deposits. The origin of these contact-metamor- 
phic deposits is conceived to be in the water and metallic substances 
which were originally contained in the magma of the porphyry, and 
which were released by decreasing pressure at the time of the intru- 
sion of the rock into higher levels of the earth's crust. We may 
thus speak of these deposits as contemporaneous with the cooling and 
solidification of the prophyry. 
As to form, the ore deposits in limestone are often irregular, but 
more frequently, perhaps, assume a tabular shape, due to the accu- 
mulation of the minerals along certain planes of stratification. 
Oxidizing waters have very greatly altered the deposits in lime- 
stone. The sulphides have been converted into carbonates, and mala- 
chite and azurite are the most common ores. Cuprite also occurs 
