Geology of Arizona. — Blake. 165 
Devonian horizon permits us to believe that we have represen- 
tatives of the Sihirian and Cambrian in the underlying strata. 
The relation of the Devonian limestones to the sub-jacent 1>eds 
is under investigation. It is believed that representatives of 
the Silurian and Cambrian systems will be found and that in 
the basal quartzytes and conglomerates we have Cambrian beds. 
Extensive outcrops of fine-grained mica and clay slates are 
found in the Dragoon uplift north of Russellville, and beyond 
northward. 
A region in the eastern part of the territor}- covered by the 
White mountain Indian reservation is as yet but little known. 
Crystalline Rocks. The underlying foundation rock in 
southern Arizona is a coarse-grained porphyritic granite which 
much resembles the typical granite of Belihen in the Vosges.""' 
This granite is found in the Santa Ritas, in the Huachucas at 
Guma, and at and beyond Oracle at the north end of the Santa 
Catalina uplift. Here it extends northward to Mammoth and 
beyond towards Riverside, the Superstition mountains and Salt 
river east of Florence. It underlies the tufas and lavas at Gila 
buttes at the head of the Florence canal. It presents generally 
a broad apparently eroded surface and here and there includes 
belts and portions of fragmentary rocks, quartzytes, and lime- 
stones, as for example in the Gold Field region east of Mesa 
and on the road from Tucson to Oracle. Large areas of gran- 
ite exist in the Bradshaw mountains, notably at and around 
Prescott. These are granite which weather into fine large 
bowlders of decomposition at Peeple's Valley, Yarapai county ; 
at points north of Phcenix, at Tombstone and other localities 
notably north of Dragoon Summit near the Wolfram veins. 
Plutonic intrusions in the form of dykes abound both in the 
crystalline and fragmentary formations. Distinct local met- 
amorphism is common where dikes of porphyry cut through 
limestone with the production of bordering masses of garnet 
rock often penetrated by copper sulphide. 
A large extinct volcano, Pinacate, rises just below the south- 
ern border near the head of the gulf of California, but it is not 
comparable in magnitude and grandeur with San Francisco 
mountain near Flagstaff and the neighboring cones dominating 
the plateau south of the grand canon. Lava streams of compar- 
* Vide the scries of typical rocks from Krantz of Bonn. 
