CHAPTER II 
GEOLOGY OF THE COAST RANGES. 
TWO DIFFERENT AXES IN.—OCCASIONAL BLENDING OP VOLCANIC ROCKS.—PREVALENCE OP FELSPATHIC ROCKS.—AGE OP THE GRANITES — 
Different strike op granitic and volcanic rocks.—Uniformity op elevation and deposit.—Climatic condition of the 
MIOCENE PERIOD.—MODE OP ELEVATION OP THE COAST RANGE.—GROUPING OP THE RANGES.—ENUMERATION OP THE RANGES, THEIR 
DIRECTION AND AXIAL ROCK.—EXTENSION OP THE RANGES SOUTH INTO THE SEA.—REAPPEARANCE IN THE CHANNEL ISLANDS.— 
Examination of the coast soundings.—Connexion op the fossils op the various strata with each other.—Dissimilarity 
TO EUROPEAN TERTIARIES OP THE MIOCENE AGE NOT NECESSARILY COEVAL IN DISTANT OCEANS.—RELATION IN FAUNA OP THE SEVERAL 
BEDS OP SOUTHERN CALIFORNIA.—EVIDENCES OP MARINE LIFE AND DEPOSITS.—DIFFICULTY OP REDUCING THEM TO ANALOGOUS ATLANTIC 
SHORE DEPOSITS.—SLIGHT OR DOUBTFUL DEVELOPMENT OP PALAEOZOIC BEDS SOUTH OF 37° NORTH LATITUDE. 
Op these mountain ranges it may be remarked that the igneous rocks which form their axes 
are of two kinds, the granitic and the trachytic. These two species, although quite distinct 
in the mode of aggregation of the mineral constituents when taken in their extreme types, yet, 
when they approach each other, not merely in topographical proximity, hut also in geo¬ 
logical age, they merge these separate differences. This has been frequently observed in the 
survey. Epidote and serpentine have been found in the granites, and in the trappean rocks of 
Monterey and San Luis counties. In Los Angeles county, along the Sierra Monica, 
amygdaloidal trachyte, and red felspar porphyry, have been seen to merge into each other, 
and the latter change into a granitoid rock. In the San Jose mountains, San Luis Obispo 
county, this last change has been frequently observed; and in the San Emilio mountain it 
has been at times difficult to say whether the rock was a granite or a trachyte, the charac¬ 
teristics of either became so indistinct. 
It may he remarked that, of the two classes of volcanic rock which correspond to the miocene 
period, that which has the felspathic type, as trachyte, trachytic porphyry, phonolite, obsidian, 
pumice, trachytic conglomerate, &c., is most commonly met in the coast mountains, or west of 
the Sierra Nevada; while the pyroxenic type, as basalt, dolerite, scoriaceous lava, &c., is 
not observed extensively distributed west, hut eastward, as in the Mojave valley, and still 
more markedly east of the Colorado river it is very abundant. 
The age of the granites of the Sierra Nevada and the Cordilleras in parallels 32°—34° is 
anterior to the eocene deposits, and posterior to the later palaeozoic; the age of the Coast Ranges 
is posterior to the miocene.* Erupted, finally uplifted, at a comparatively late period in the 
history of our planet, it might he expected that the lines of direction of the forces of both ranges 
would he somewhat similar ; they so far correspond as to have a common direction north and 
* The writer desires that his ideas on the antiquity of California igneous rocks may not be misunderstood. The age of an 
axial rock combines the idea of its first upheave through the hardened crust, and, to some extent, the period of its appearance 
above water, though not necessarily the latter idea. The Coast Ranges were upheaved and uplifted above water posterior to 
the miocene deposit; but the Sierra Nevada were upheaved some thousand feet through the crust anterior to the eocene ; the 
crested summit was, in all probability, from 1,000 to 2,000 feet above water during the miocene, and its final uplift was in all 
probability subsequent to the quaternary deposits on its slopes—both those of San Bernardino plains, and those of the Mojave 
valley. 
T. A. 
