gg OKAND CANON DISTEICT. 



flex ed Cretaceous .,a = ^ J^ti -^g^ 



e ™l land, or a little within, Its marginal portions. 

 ThoTwt iH-runl of deposition was .narked by the accumulation the 

 Eocene td'hieh form soon a striking feature in the stradgraphy o 



LocuieLKCLs, plateau countrv. Around the southern Hanks 



the peripheral parts ot the L latum country, 

 of the Uintas their aggregate thickness exceeds 5,<XK u< t, bits 

 wa «l the upper members disappear, and 80 miles north ot the Grand 

 non only about 1.000 to 1,200 feet, representing the lowest port .on oi 

 hl^nak, their appease, It is highly probable that then. Id, 

 and upper portions of the Eocene W ere never deposited there, But he 



tow J beds, most probably, once covered the entire province, wh.lo the, 

 middle and late Eoeenewere confined to its more northerly portions 

 The lowest members were deposited in brackish water, as their loss. Is 

 amply attest; but in the succeeding beds the fossil forms are ent.rel.v 

 those which live in fresh water. From that epoch to the present tune 

 there has been no recurrence of marine conditions. 



We now reach a turning point in the history of this region, iliat 

 long continuance of marine conditions lasting from the beginning ot 

 Carboniferous time to the close of the Cretaceous came gradually to an 

 end. The waters became brackish and then fresh. During the preva- 

 lenceof the marine condition it seems to be a necessary conclusion that 

 the waters which covered it had abundant access to the ocean. Whether 

 its waters were wide open to the ocean, like the Gulf of Mexico or Hud- 

 son's Bay, or whether they formed a broad expanse, with a compar- 

 atively narrow outlet, like the Mediterranean, we do not know, and it 

 would be useless to conjecture at present. At all events the communi- 

 cation was sufficiently free to maintain a degree of saltness suitable to 

 the existence of molluscan forms of the ordinary marine types. When 

 i he waters became brackish, we infer that the straits became greatly 

 narrowed; when they became quite fresh, we infer that the access of the 

 ocean to the area was wholly shut off, and that the water brought by 

 the rivers and rains merely outflowed, and the region became an inland 

 lake of vast proportions. For the deposition still went on. Through 

 Eocene time from 1,000 to 5,000 feet of lacustrine beds, containing an 

 abundance of fresh-water fossils, were deposited. Among them are also 

 found layers of coal and carbonaceous shales, and sandstones thickly 

 imprinted with the traces of arboreal vegetation. 



But at length the deposition of lacustrine strata ceased ; not, however, 

 at one and the same time in all parts of the province. The evidence indi- 

 cates that in the southern and southwestern portions it stopped after 

 about one-fourth or one-third of the Eocene horizons had been laid down. 

 In the central portions it appears to have ceased after about one-half 

 to two-thirds of those horizons had been deposited. In the northern 

 portions, in the vicinity of the Uintas, the entire system of Eocene 



