458 



MESOZOIC TIME. 



Upper Missouri region. The group extends from Southern Colorado northward beyond 

 the United States boundary, and hence has a length exceeding 1,000 miles, with an 

 average width of 500 miles (C A. White). The Wahsatch range is its western boun- 

 dary. In their sandy nature the beds closely resemble those of the Fox Hills group. 



It is also possible that the Tejon group, the coal-bearing group of California, is an 

 equivalent of the Wyoming coal series or Laramie group. Gabb states that a species of 

 Ammonites extends through the group to the veiy top, and affords strong evidence of its 

 Cretaceous age ; and this is made stronger by the occurrence also of three or four spe- 

 cies of the Chico group in the Tejon group, e. g., Mactra {Cymbophora) Ashbumerii 

 Gabb., Nucula truncata Gabb., Avicula pellucida Gabb. To show the Tertiary aspect 

 of the shells, the genera are enumerated on page 508. Conrad referred the California 

 beds to the Eocene. 



The Vancouver Island Cretaceous contains workable beds of coal, and has afforded 

 Inocerami, Trigonice, Ammonites, Baculites, Belemnites, and other Cretaceous fossils. 



Economical Products. 



Mines of Cinnabar, the chief ore of quicksilver, occur at various 

 points in the metamorphic Cretaceous rocks of the Coast ranges of 

 California. The usual associated rocks are serpentine and argillaceous 

 and siliceous slates. The most productive region is that of ftew 

 Almaden, fifty miles south-southwest of San Francisco. It is worked 

 also at New Idria, in Fresno County, at the Reddington mine in Lake 

 County, and at some other points. 



The Coal-beds, whether Cretaceous or Tertiary, are of great value 

 to the country. They are described under the Tertiary. 



Gold is found sparingly in the metamorphic Cretaceous of California, 

 but has not repaid working. Copper also occurs in many localities, 

 but not in workable veins. Chromic iron is found in the serpentine 

 of California, but not in a condition to repay mining. 



The Green S<md has already been mentioned as a valuable fertilizer. The green 

 grains (called also Glauconite) consist of about 50 per cent, of silica, 20 to 25 protoxyd 

 of iron, 8 to 12 potash and soda (mostly potash), and 7 to 10 water, with also a trace of 

 phosphate of lime. For analyses, see author's "Treatise on Mineralogy." 



II. Life. 



1. Plants. 



With the opening of the Cretaceous period, we find indicated in the 

 rocks a great change in the vegetation of the continent. The Cycads 

 of the Triassic and Jurassic still existed, but they were accompanied 

 by the first yet known of the great modern group of Angiosperms, — 

 the class which includes the Oak, Maple, Willow, and the ordinary 

 fruit trees of temperate regions, — in fact, all plants that have a bark, 

 excepting the Conifers and Cycads. More than one hundred species 

 have been collected ; and half of them were allied to trees of our own 

 forests — the Sassafras (Fig. 825), Tulip Tree (Fig. H?,Q), Plane (or 



