208 QUICKSILVEU DEPOSITS OF THE PACIFIC SLOPE. 



Bernardino, and San Diego Connties, into Lower California and along 

 the peninsula to within a few miles of the old mission of Santa Gertrudis, 

 while, from the exposure through denudation at Santa Gertrudis and again 

 near Loreto, it is proljable tliat between the mission and Cape San Lucas 

 the granite nowhere lies at a greater depth than 1,000 feet. Dr. White has 

 pointed out that fossils of the Atlantic Cretaceous founa, which is entirely 

 distinct from the fauna of the Pacific Cretaceous, are found on the western 

 side of the Sierra Madre of Mexico, thus showing that Lower California 

 was during the Cretaceous the dividing isthmus between the oceans and 

 confirming Gabb's view. 



Though tlie iirobabilities are thus strongly in favor of the theory that 

 the Cascades and the mountains of Lower California are the main struct- 

 ural continuations of the united Sierra and Coast Ranges, it by no means 

 follows that these ranges form an isolated s}'stem or that these continua- 

 tions of the California mountains are the only ones. On the contrary, 

 there is nuich evidence that the Sierra is inseparable from the basin sys- 

 tem, which appears to continue through Arizona and to nnite with the 

 Rocky Mountain system. Too little is known of northern Mexico and 

 the territory of the United States immediately adjoining it to justify any 

 extended speculation on this subject. 



Pre-Cretaceous upheavals and metamorphism. TwO iuipOrtaUt arCaS of SCrpentiuized 



and silicified, metauiorphic rock.s have been shown in the foregoing pages 

 to be of the same age, probably Neocomian, and it has been established 

 that these series wei-e upheaved and metamorphosed prior to the deposition 

 of the Wallala beds, regarded by Dr. White as Turonian. But there are 

 other metamorphic rocks in California deposited long before the Neocomian. 

 Thus the Carboniferous limestones on the McClond River are crystalline 

 and the metamorphic shales near Pence's ranch, in Butte County, are at 

 least in part Carboniferous. They bear considerable similarity to those of 

 the Mariposa group, and, furthermore, they are nearly vertical and strike in 

 nearly the same direction as those of the gold belt proper. The question 

 therefore at once arises whether their upheaval and metamorphism are 

 ascribable to the same period as the uplift and alteration of the Mariposa 

 and Knoxville beds. 



