58 



LARAMIE FLORA OF THE DENVER BASIN. 



there is stratigraphic connection, the post-Montana fades 

 would be even more apparent. In the latter area are 

 found such distinctively post-Montana forms as Zkyphus 

 fibrillosus, Cinnamomum affine, Populus meehiif, Populus 

 monodon, Viburnum wntorlum, etc., which have not 

 been noted in the Grand Mesa field. This but emphasizes 

 the fact that the collections of plants are too meager and 

 obviously incomplete to enable us .to reach thoroughly 

 conclusive results, though when fuller collections are 

 obtained, as in the Glenwood Springs area, the resemblance 

 to higher beds is accentuated. 



GRAND HOGBACK AND DANFORTH HILLS AREA, 

 COLORADO. 



The important coal area of the Grand Hog- 

 back and Danforth Hills lies along the eastern 

 rim of the Uinta Basin and i§ in direct strati- 

 graphic connection with the Glenwood Springs 

 area, on the southeast, while to the west it 

 passes with ' some interruptions into the less 

 important coal field of Uinta County, Utah. 

 This general region was -visited in 1872 by S. F. 

 Emmons, 8 of the Fortieth Parallel Survey, and 

 in 1876 and 1877 by C. A. White, 9 of the Hay- 

 den Survey. White referred the coalrbearing 

 rocks of this region to the Fox Hills and Lara- 

 mie. The Fox Hills, in accordance with what 

 he called the "modified classification of the 

 Cretaceous strata adopted in this report," 

 „ included both the Pierre and Fox Hills of the 

 Missouri River section and was regarded as of 

 Cretaceous age, while the Laramie was classed 

 as post-Cretaceous and was supposed to be 

 transitional between Cretaceous and Tertiary. 



A number of other reports on the coal re- 

 sources of the region by Chisholm, Hills, 

 Storrs, Hewett, and others do not need special 

 mention in this connection. 



This field was studied by H. S. Gale 10 in 

 1906, and the final results in this and other 

 related areas in northwestern Colorado and 

 northeastern Utah were published in 1910." 

 The section as worked out by Gale is essentially 

 the same as that in the Book Cliffs, Grand 

 Mesa, and Glenwood Springs fields — that is, 

 the Mesaverde formation was regarded as the 

 uppermost or youngest formation of the Upper 

 Cretaceous section in this part of the basin. 

 The divisions established by Lee in the Grand 

 Mesa region were not recognized by Gale, 



s U. S. Geol. Expl. 40th Par. Rept., vol. 2, pp. 167-189, 1877. 



• U.S. Geol. and Geog. Survey Terr. Tenth Ann. Rept., for 1876, pp. 

 5-60, 1878. 



i° Coal fields of the Danforth Hills and Grand Hogback, in northwestern 

 Colorado: U. S. Geol. Survey Bull. 316, 1906, p. 264, 1907. 



ii Coal fields of northwestern Colorado and northeastern Utah: U. S. 

 Survey Bull. 415, 1910. 



though he divided the Mesaverde into lower and 

 upper members, the line of separation being in 

 many parts of the field a conspicuous white 

 sandstone. The character of the two members 

 was described as follows: 



Fossil invertebrates have been found in almost all parts 

 of the Mesaverde formation. They indicate that the lower 

 part is largely of marine origin, up to and probably Jp- 

 cluding the "white rock." Above the "white rock" 

 fresh and brackish water invertebrates and plants indicate 

 a change of character in the body of water in which the 

 succeeding beds were formed. The fresh or hrackish 

 water conditions, however, were not. permanent and gave 

 way to true marine conditions again near the top of the 

 formation. 



The absence of the Lewis shale and the 

 "Laramie," both of which are present in the 

 adjacent Yampa field, may of course be ex- 

 plained in either of two ways — that is, they 

 may never have been deposited in this basin, 

 or, if deposited, they may have been removed 

 by erosion. The fossil plants, so far as they 

 have been discussed in published reports, ap- 

 pear to be of Mesaverde types, but there is 

 some evidence not yet published that suggests 

 the possibility that the Laramie also may be 

 represented here. Be this as it may, however, 

 the' Laramie is not now recognized as present 

 in the Grand Hogback and Danforth Hills 

 fields, or, indeed, in the Uinta Basin. 



The conditions just described may be traced 

 westward from the Danforth Hills, except that 

 the unconformity separating the Mesaverde 

 from the overlying Tertiary appears to cut 

 deeper and deeper. Thus at Vernal, Utah, the 

 Mesaverde is only about 1,500 feet thick, and 

 the upper coal-bearing portion is thought to be 

 absent, and in the Deep Creek district in Uinta 

 County, Utah, the whole of the Mesaverde has 

 apparently been removed. Reports on sev- 

 eral of these fields have been made by Gale, 12 

 Lupton, 13 and others, but as the Laramie is not 

 involved, they may be passed over. 



GREEN RIVER BASIN. 

 YAMPA COAL FIELD, COLORADO. 



The Yampa field, which occupies a consid- 

 erable area in Routt County, Colo., lies along 



i 2 Gale, H. S., Coal fields of northwestern Colorado and northeastern 

 Utah: U. S. Geol. Survey Bull. 415, pp. 179-219, 1910; Geology of the 

 Rangely oil district, Rio Blanco County, Colo.: U. S. Geol. Survey Bull 

 350, 1908. 



u Lupton, C. T., The Deep Creek district-of the Vernal coal field, 

 Uinta County, Utah: U. S. Geol. Survey Bull. 471, p. 579, 1912; The 

 Blacktail (Tabby) Mountain coal field, Wasatch County, Utah: Idem, 

 p. 595. 



