378 W. ('. KNIGHT — JURASSIC ROCKS <>!•' SOUTHEASTERN WYOMING 



In southeastern Wyoming, or that portion of the state lying east of 

 the South Platte liver and south of the Fremont, Elkhprn and Missouri 

 Valley railroad, the Jurassic rocks are exposed in numerous places. 



Early I nvestigators 



Doctor Hayden refers to the Jurassic* rocks of the Laramie moun- 

 tains as follows : 



" Resting above the Red beds is a series of marls and arenaceous mails of light 

 or ashen gray color, with harder layers of limestone or fine sandstone, which were 

 also first discovered around the margin of the Black hills in Dakota in 1857. Since 

 the discovery in the Black hills, Jurassic fossils have been found over a very wide 

 geographical area, and yet J have never seen them so well developed, or the pecu- 

 liar fossils so abundant, as at the locality where they were first observed. Although 

 1 have traced this Jurassic belt by its organic remains over many hundreds of 

 miles, I have been able to discover scarcely a well defined Jurassic fossil south 

 of Deer creek, a point 100 miles north of Fort Laramie and south of lake Como on 

 the Union Pacific railroad." 



The Fortieth Parallel Survey f reported Jurassic rocks on the Laramie 

 plains as follows : 



"Jurassic rocks occur from Red Buttes southward to Red lake, usually showing 

 but limited outcrops, and those confined chiefly to the calcareous portions of the 

 series. Upon the summit of the high Triassic plateau southeast of Red Buttes are 

 exposures, about 200 feet thick, of Jurassic rocks, the summit members having 

 been eroded off. Beginning at the top, the beds are as follows : A sandstone body 

 100 feet thick, white and friable at the top, reddish brown, slightly intercalated 

 with variegated clays and marls in the middle, passing downward into cream 

 colored, marly sandstone; beneath this is 25 feet of bluish gray, cherty limestone, 

 followed by 75 feet of bluish white sandstone, which rests upon the yellowish red, 

 cross-bedded sandstones of the top of the Trias. 



"At the dome-like quaquaversal at the northern edge of map I, near the 100th 

 meridian, at Como, the easily recognized Dakota sandstone and conglomerates 

 overlie a series of Jurassic rocks, which are exposed from 175 to 200 feet. Passing 

 downward from the base of the Dakota Cretaceous, the Jurassic rocks consist of 

 li ret, gray clays and sandy marls, containing a great many gritty particles of angular 

 silicious sand ; secondly, creamy marls, with thin, sandy layers; thirdly, bluish 

 drab, cherty limestones ; fourthly, fine ash colored marls, with thin beds, varying in 

 thickness, of light colored limestones ; fifthly, gray and orange colored marls, with 



* Ueological Survey of Wyoming and contiguous territory, 1870, pp. 21, 22, 28. See also Lieuten- 

 ant G. K. Warren: Preliminary Report of Explorations in Nebraska Territory and Dakota, 1855- 

 'fitt-'57. J>. I>. Meek and F. Y . Hayden : Paleontology of the upper Missouri; numerous refer- 

 ences I" type species discovered along the North Platte river, especially near lied Butte. 



t Clarence King: Systematic Geology, Fortieth Parallel Survey, 1878, pp. 2Sti-28T ; also Geolog- 

 ical Survey of the Territories, F. V. Hayden, I8G7-'69, pp. 82,89,113; also Geological Surveyed' 

 Wyoming and contiguous territory, LS70, p. 131. 



