Nature and science on the Pacific coast : a guide-book for scientific travelers in the West . a. llie historyof the relatively recent periods, of the geologicyesterday, is written in more detail than elsewherein the world. It treats of marine, terrestrial, andglacial conditions, of the base leveling of mountainranges followed by vulcanism, earth movementsand the re-birth of mountain systems. In the attempt to select and describe a few ofthe salient features of this long and complicatedhistory, it has been difficult to make the treatmentaccurate, or to give alternate interpretations whichmay be
Nature and science on the Pacific coast : a guide-book for scientific travelers in the West . a. llie historyof the relatively recent periods, of the geologicyesterday, is written in more detail than elsewherein the world. It treats of marine, terrestrial, andglacial conditions, of the base leveling of mountainranges followed by vulcanism, earth movementsand the re-birth of mountain systems. In the attempt to select and describe a few ofthe salient features of this long and complicatedhistory, it has been difficult to make the treatmentaccurate, or to give alternate interpretations whichmay be as worthy of consideration as those pre-sented here. The limited space allotted to thisarticle has rendered it inadvisable to cite the con-tributions of each of the geologists who have addedto our knowledge of west coast geology. The briefbibliography includes a few important papers bear-ing on the subjects emphasized in this the accompanying geological map the formationshave been grouped according to the divisionsadopted in the text of this article. (See Pis. XXXIXand XL.) 41. 42 Figrure 5 Geology of West Coast Region of United States The Pre-Cambrian of the West Coast.—For-mations of pre-Cambrian age doubtless exist innumerous localities in this region, but in most casesthe proof of the suspected antiquity of these stratais lacking. East of the region under consideration,intense and widespread metamorphism is generallyconsidered a proof of great geological age. In thePacific region such metamorphism merely indicatesan age antedating the intrusion of the Sierra Nevadabatholith. Patches of known pre-Cambrian occur north-west of Owens Lake, where a metamorphosed seriesappears underneath strata carrying an Olenellus(lower Cambrian) fauna. Numerous areas of prob-able pre-Cambrian occur in the desert mountainranges of the region adjoining Arizona, as provedpre-Cambrian is found in the Grand Caiion of theColorado, and neighboring areas. All other com-ponents of these r
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