CHAPTER II. 



GEOLOGY OF THE COAST RANGES. 



two different axe3 in. — occasional blending op volcanic rocks. — prevalence of felspathic rocks. — aoe of the gravites — 

 Different strike of granitic and volcanic rocks. — Uniformity of elevation and deposit. — Climatic condition of the 



MIOCENE period. — MoDE OF ELEVATION OF THE COAST RANGE. — GrOUPIN'G OF THE RANGES. — EnOMEBATION OF THE RANGES, TBEIB 

 DIRECTION AND AXIAL ROCK. — EXTENSION OF THE RANGES SOUTH INTO THE SEA. — ReAPPEAKANOE IN THE CHANNEL ISLANDS. 



Examination of the coast soundings. — Connexion of the fossils of the various strata with each other. — Dissimilaritt 



TO EUROPEAN TERTIARIES OF THE MIOCENE AGE NOT NECESSARILV COEVAL IN DISTANT OCEANS. — RELATION IN FAUNA OF THE SEVERAL 

 BEDS OF SOUTHERN CALIFORNIA. — EVIDENCES OF MARINE LIFH AND DEPOSITS. — DIFFICULTY OP REDUCING THEM TO ANALOGOUS ATLANTIC 

 SHORE DEPOSITS. — SLIGHT OR DOUBTFUL DEVELOPMENT OF PAL.EOZOIC BEDS SOUTH OF 31° NORTH LATITUDE. 



Of these mountain ranges it may be remarked tliat tlie 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 typen, 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 tiie Saa 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 be 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, «fec., 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, but 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° — 3d° is 

 anterior to the eocene deposits, and posterior to tlie later pala30zoic ; the age of the Coast Kanges 

 is posterior to the miocene.* Erupted, finally uplifted, at a comparatively late period in the 

 history of our planet, it might be expected that the lines of direction of the forces of both ranges 

 would be 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 roclis may not be misunderstood. The ag^e 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 waler, 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. 



