METAMORPHIC ROCKS—LIMESTONE—GRANITE. 201 
exposed. It is much stained and rusted by the decomposition of iron pyrites, which probably 
exists in an unaltered state a few feet below the surface. 
Between the western ridge just described and the main ridge of the Sierra there are several 
granitic outcrops of small extent rising at intervals from the plain, showing that it is under- 
laid at only a slight depth by an uneven surface of granite. All the minor inequalities of the 
surface have been filled, and the rocks buried from sight, by the drift deposits of sand, gravel, 
and boulders that form the slope. These isolated outcrops conform in their general structure, 
trend, and dip to the ridge already described. A more compact rock, a gray granite, with the 
planes of structure obscurely developed, is also found. The outcrops of the rocks bordering the 
valley on the north are much obscured by a covering of drift, or similar accumulations; but 
wherever they were exposed to view a laminated structure was visible. They are nearly all 
gneissose, and less hard than the dense hornblendic rock of a part of the western ridge. 
Section at the Tejon Ravine.—A good natural section, about three miles in length, is formed 
by the creek that flows from Tah-ee-chay-pah prairie to the Tejon. Its general direction is east 
and west, which is nearly at right angles to the trends of the structural planes of the granitic 
rocks. The general character of the rock may be understood by referring to the section, (Section 6, 
Sheet IV.) The fine lines are intended to represent the lamination and structural characters. It 
is, of course, impossible to make a perfect miniature representation of the rock, or to show the 
numerous plications and curves that exist. Hundreds of lines are contained in a single foot of 
rock ; while in the section over five thousand feet are represented in the space of a single inch. 
The first part of the exposed rock at the entrance to the ravine contains a large proportion of 
mica, and numerous feldspathic veins; in some places it is highly laminated, and much flexed 
and contorted, presenting various dips at different distances below the summit. The foldings 
and contortions are well developed on a small scale, and at the same time are subordinate parts 
of more extended curves and plications. A short distance beyond station 52, and on the south 
side of the ravine, there are indications of an outcrop of white crystalline limestone. Its 
junction with the granitic rocks is covered by earth, so that its extent and position could not be 
exactly determined ; but that it exists in considerable quantities is shown by the loose masses 
that roll to the foot of the hill, and abound in the small cañons and ravines at its base. This 
limestone will be found valuable for making caustic lime for buildings on the Military Reserve, 
and other settlements in the vicinity. 
Beyond this, and on the north side of the ravine, the granitic rock becomes more compact 
and contains hornblende, but retains its laminated structure. About station 40, mica is 
abundant, and the rock is gneissose and much contorted. "Towards the summit, the rocks grow 
More compact and less highly laminated ; they contain less mica and are more like ordinary 
granite. "Wherever this compact rock is fully exposed to the action of the weather it presents 
rounded outlines, instead of the ragged and angular surfaces that characterize the more slaty and 
laminated portions. 
The minerals which form this granite are feldspar, quartz, hornblende, and mica; the two 
latter appearing to be the varying constituents, and either found together in like proportions, 
Or one predominating over the other without producing any great change in the appearance of 
the rock. It resembles syenite, and has a very even texture, and light, gray color. There is, 
however, an abundant distribution throughout the mass of isolated patches of a darker color 
than the surrounding portions; and these masses have a lenticular or elongated form, and 
Preserve a general parallelism of direction , corresponding with that of the planes of structure in 
26 F 
RUNS a eg RUE‏ 3 اون 
