i(b. 1.] GEOLOGf AN£) MiXEriAtOGf. 113 



East of the California Valley lies the Sierra Nevada ; a lofty 

 mountain chain reaching all the way from our northern to our 

 southern boundary. The crest of the Sierra Nevada is so high 

 and continuous that for a thousand miles it shows no passes less 

 than five thousand feet above the sea, and yet, at three points 

 there are gate-ways opened in this wall, by which it may be passed 

 but little above the sea-level. These are the canons of the Sacra- 

 mento (Pit River), the Klamath, and the Columbia. All these 

 are gorges cut through this great dam by the drainage of the 

 interior of the continent. In the lapse of ages the cutting down 

 of this barrier has progressed to such an extent as almost completely 

 to empty the great water basins that once existed behind it, and 

 leave the interior the arid waste that it is — the only real desert on 

 the North American Continent. 



The Sierra Nevada is older than the Coast Mountains, and was pro- 

 jected above the ocean, though not to its present altitude, previous 

 to the Tertiary nnd even Cretaceous ages. This we learn from the 

 fact, that strata belonging to these formations cover its base, but 

 re ich only a few hundred feet up its flanks. The mass of the 

 Sierra Nevada is composed of granitic rocks, associated with which 

 are metumorphic slates, proved by the California Survey to be of 

 Triassic and Jurassic age. These slates are traversed in many 

 localities by veins of quartz, which are the repositories of the gold 

 that has made California so famous amon2; the minino; districts of 

 the world. 



East of the Sierra Nevada we find a high and broad plateau, 

 five hundred miles in width, and from four thousand to eight 

 thousand feet in altitude, which stretches eastward to the base of 

 the Rocky 3Iountains and reaches southward far into Mexico. Of 

 this interior elevated area the Sierra Nevada forms the western 

 margin, on which it rises like a wall. It is evident that this 

 mountain belt once formed the Pacific coast; and it would seem 

 that then this lofty wall was raised upon the edge of the continent 

 to defend it from the action of the ocean waves. In tracing the 

 sinuous outline of the Sierra Nevada, it will be seen that its crest 

 is crowned by a scries of lofty volcanic cones, and that one of these 

 is placed at each conspicuous angle in its line ot bearing, so that it 

 has the appearance of a gigantic Ibrtification of which each salient 

 and re-entering angle is defended by a massive and lofty tower. 



The central portion of the high table lands, to which I have 

 referred, was called by Fremont the Great Basin, from the fact 

 YoJ. vi, H Ko. 1. 



