4G0 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



That the primeval rocks must nnderlie all others is self-evident and the 

 lowest rocks we know of are granitic. It has never been shown liow tlio 

 ori^'inal crust could he whoUv hin-ied benoatli its own ruins, and sim[)lc 

 arguments are adduced to sliow this utterly improbable. It follows that a 

 part of the granite nuist be Azoic and that the lavas which have lu'oken 

 tln-ough the granite cannot l)e remelted sediments. 



Historical geology. — Tlic followlug outliue states iu the Ijriefest terms the 

 main events in the geological history of the Coast Ranges, so far as they 

 have been elucidated by former observers and by nn^self 



Prior to the opening of the Cretaceous the region of the Coast Ranges 

 seems to have been chiefl}' occupied by granite. Daring the first period 

 of the Cretaceous — the Neocomian — great rpiantities of sediments derived 

 from the granite were deposited on the quicksilver belt. These were chiefly 

 sands, though shales and calcium carbonate were also found. The sea nuist 

 have been shallow and many islands nnist have existed in it. The most 

 characteristic animals of the })eriod werc^ Aiirclhi amceiifrira and AiiccJIa 

 mosf]nciisl<!, of which a descrijjtion, with illustrations, by Dr. C. A. Wiiite, is 

 "■iven in Chapter V. At the close of the Neocomian an upheaval took 

 place with extraordinary violence, folding and crushing the rocks and pro- 

 ducing the first ranges along the coast of California of which any record 

 remains. It is probable enough that earlier ranges existed, l)ut had been 

 obliterated. The same upheaval affected the Sierra Nevada and added to 

 its western side, along a part of the gold belt, an immense mass of Neo- 

 comian rocks, which were driven into a nearly vertical position. Accom- 

 panying this upheaval was a vast expenditure of energy. The heat into 

 which this energy was converted brought about the solution of some 

 components of the underlying granite, particularly of magnesia and soda. 

 These solutions, acting on the Neocomian rocks, converted them into the 

 metamorphic product mentioned in preceding paragraphs. 



During the jMiddle Cretaceous (the Turonian) the shore of California 

 seems to have been nearly in the same position as it now is, and a series 

 of beds discovered during this investigation, the Wallala group, was de- 

 posited. They are composed of granitic detritus and fragments of meta- 

 morphosed Neocomian beds and certain fossils. 



