GEOLOGICAL SKETCH OF THE REGION OF TUCSON. 47 
tains, a high and nearly parallel range farther east, they represent a large 
part of the southward continuation of the Bradshaw Mountains of Cen- 
tral Arizona. 
The central nuclei of these ranges consist of crystalline rocks, chiefly 
granitic and gneissic. 
The rock formations on the southern side of the Catalinas, toward the 
valley of Tucson, are for the most part pre-Cambrian gneiss and mica- 
schists in tabular form, regularly stratified and with included sericitic 
schist, all believed to represent some of the oldest rocks known, equiva- 
lents of the ancient Huronian, the Keweenawan, and Laurentian forma- 
tions of Canada. 
The complete penetration of the schistose slates by veins and layers of 
potash or soda feldspar, forms what is known as ‘‘augen-gneiss,’’ so called 
because of the many white protuberances on the surfaces. This rock, 
particularly near the mouths of Sabino and Bear canyons, can be broken 
out in tabular masses well adapted to constructive purposes. It also 
can be quarried in prismatic or post-like blocks from 3 to 4 feet long, such 
as were utilized by the prehistoric people for foundations of houses by 
setting them upright in the ground, as may be seen in the remains of an 
extensive village at the mouth of Bear Canyon. 
Pre-Cambrian gneissic rocks are also largely developed on the north- 
eastern flanks of the Catalinas, and are there associated with highly 
laminated mica-schists; the Arizonian, a formation largely developed at 
several widely separated localities in southern Arizona, notably at Pinal 
and the Salt River Valley. These schists are characterized by extreme 
foliation and sharp angular plications presenting zigzag lines upon 
exposed surfaces. 
Here also, on the northeastern side of the Catalinas, we find Paleozoic 
strata resting uncomformably upon the crystalline schists of the pre- 
Cambrian, or upon a broad area of coarse granite as at Oracle and at the 
sources of the Canada de Oro on the northeast side of the range. 
The foundation granites are penetrated by great dikes of diorite 
which, coming in contact with limestone of a dark bluish-gray color, have 
changed it to a crystalline white marble, seen to good advantage at Gies- 
man’s Camp and Marble Peak. Copper ores are developed along the 
contact, notably at the Apache Spring and Leatherwood’s Camp. 
DEVONIAN ROCKS. 
Between the Southern Belle Canyon and Pepper-Sauce Gulch, a 
high and long ridge extending eastward and named Coral Ridge is made 
up of quartzite, limestone, and shaly limestones in which there is a bed 
of corals and shells of Devonian age. These fossils are interesting, not 
only as evidence of the geological age of the rocks and records of the life 
of that early period, but for their wonderful preservation in every detail 
