HISTORICAL KEVIEW OF THE LAKAMIE PROBLEM. 



59 



the southern border of the Green River Basin 

 and is separated from the Uinta Basin by an 

 anticlinal axis that extends from the Uinta 

 Mountains eastward to the Rocky Mountains. 

 At one point in Axial Basin only about 4 miles 

 intervenes between the Yampa and Danforth 

 Hills fields, yet the sections of coal-bearing rocks 

 in the two areas, as published, are considerably 

 different. 



The Yampa field was studied by members of 

 both the King and Hayden surveys, and the 

 coal-bearing rocks were in large part referred 

 to the Laramie, a reference that became more 

 and more firmly fixed as time went on; in fact, 

 the whole coal-bearing section was accepted as 

 of this age until about 1905. In that year this 

 field was investigated by Fenneman and Gale," 

 who were able to divide the Cretaceous portion 

 of the coal-bearing rocks into three forma- 

 tions — the Mesaverde, which was believed to 

 correspond in whole or in part to the beds so 

 named in southwestern Colorado; the Lewis 

 shale, a marine formation of soft shales and 

 sandstones overlying the Mesaverde; and the 

 Laramie. Tlus field, together with the others 

 to the south, was more fully considered by 

 Gale '^ in 1910. 



The "Laramie" in the Yampa field was de- 

 scribed as being about 1,200 feet thick and 

 composed of relatively soft sandstones and 

 shales. It was said to be limited at the top 

 by an unconformity that separates it from 

 overlying Tertiary beds, also coal-bearing, 

 which are probably to be regarded as Fort 

 Union or its ef[uivalent. The base of the 

 "Laramie" — that is, the line separating it 

 from the Lewis — was apparently established 

 with difficulty; in fact, it appears to have been 

 drawn arbitrarily in this field. On this point 

 Gale said: 



A8 mapped, the formation is intended to represent a 

 group that is distinguished from those adjacent by a 

 difference of rock composition and that may be recognized 

 by this distinction in the field. In the case of the Lara- 

 mie the featirre that distinguishes it from the underlying 

 Lewis shale is the presence of sandstone beds that form 

 prominent ridges or ledges in the topography. Unfor- 

 tunately the horizon of its lowest sandstone does not appear 

 to be constant in different parts of the field, so that if it 

 were possible to fix on a singje definite plane as marking the 

 basal member of that formation and trace it throughout the 



'< Fenneman, N. M., and Gale, H. S., The Yampa coal field, Routt 

 County, Colo.; U. S. Geol. Survey Bull. 297, 1906. 



IS Gale, H. S., Coal fields of northwestern Colorado and northeastern 

 Utah: U. S. Geol. Survey Bull. 415, 1910. 



field, it would not everywhere lie in the same relation to 

 the lowest of the principal group of sandstones overlying. 

 Furthermore, though the formation as a whole is consid- 

 ered to mark the transition from marine to brackish and 

 fresh water deposits, the fossils found in the lowest part of 

 the sandstones included in the Laramie, including those 

 in the massive sandstone beds, are distinctly marine and 

 include a fauna apparently not distinguishable from that 

 of the Lewis beneath. 



North of Craig the relations at the base of 

 the "Laramie" appear to be particularly un- 

 certain. Gale stated: 



The base of the Laramie formation has been assumed to 

 be at the base of the ledge that forms the prominent cliff 

 or rock wall just north of the town. The outcrop of this 

 stratum may be traced almost continuously for about 6 

 miles west of Craig, but beyond that it is concealed by 

 the overlapping deposits of the Browns Park formation. 

 Similar beds are again revealed farther west. * * * In 

 that region the identity of the horizon already adopted as 

 marking the base of the Laramie is, however, much in 

 doubt. 



LITTLE SNAKE RHTER AREA. WYOMING AND COLORADO 



The area drained by Little Snake River ex- 

 tends from the Sierra Madre westward to the 

 Red Desert, and from the summit of the Elk- 

 head Mountains in Colorado northward to the 

 divide separating this area from the Great 

 Divide Basin, which is just south of the L'nion 

 Pacific Railroad. It is separated by the Elk- 

 head Mountains from the Yampa field, con- 

 sidered above. 



The western part of this field was studied by 

 M. W. Ball '" in 1907, and the eastern part by 

 Ball and Stebinger " in 1908. The section is 

 essentially the same as that of the Yampa 

 field and also of the field studied by A. C. 

 Veatch in east-central Carbon County. As 

 these areas will be considered in detail in dis- 

 cussing the relations between the Laramie of 

 the Denver Basin and the so-called "Lower 

 Laramie" of Veatch, no further mention at 

 this point is necessary. 



CARBON COUNTY, WYOMING, AND ADJACENT AREAS. 



An extensive area Ij'ing mainlj in east- 

 central Carbon Count}', Wvo., just east of 

 the Green River Basin and forming the west- 

 ern part of what has sometimes been desig- 

 nated the Laramie Plains, is a structural 

 and geologic basin lying in the angle where 



'" Ball, M. W., The western part of the Little Snake River coal field, 

 Wyo.: r. S. Geol. Survey Bull. 311, p. 243, 1909. 



" Ball, M. W.,and Slcbinger, Eugene, The eastern part of the Little 

 Snake River coal field, Wyo.: U. S. Geol. Survey Bull. 381, p. 186, 1910. 



