stanton.] NEW MEXICO AND COLORADO. 31 



brownish bituminous and calcareous shales. Inoeeramus Jabiatus and 

 Gryjylicm newberryi 1 range from bottom to top of this series, and in the 

 upper portion. Inoeeramus fragiliSj Ostrea congesta, O.clegantula, Priono- 

 tropis woolgari, etc., also occur. 



In western New Mexico and southwestern Colorado the Cretaceous 

 section contains no limestones, or only very thin bands of local extent 

 that are seldom exposed, and the same statement will apply to the 

 entire area between the Continental Divide and the Wasatch moun- 

 tains. The calcareous beds of the Niobrara division that have served 

 as a convenient reference plane in all the region east of the mountains 

 are absent. The section in the area drained by the San Juan river 

 naturally falls into three lithologic divisions, the lowest of which is a 

 series of coarse sandstones, with some beds of shale, and in the upper 

 portion one or more coal beds. The middle division consists of dark 

 clay shales, 1,200 to 1,500 feet in thickness, and is overlain by a thick 

 series of coal-bearing sandstones, shales and marls forming the upper 

 division. These are the members of Dr. Newberry's general section, 2 

 and similar divisions have been made by other geologists who have 

 described the region, though they have sometimes been still further 

 subdivided, and there have been differences of opinion as to the corre- 

 lation of certain parts of the section with the formations east of the 

 mountains. All have agreed, however, that the sandstones at the base 

 (or at least the upper part of them) belong to the Dakota formation 

 and that the Colorado formation is represented in the shales of the 

 middle division. 3 



Here and in other portions of western Colorado the larger part of the 

 coal bearing sandstones and shales of the upper division was referred 

 to the Fox Hills group by the members of the Geological Survey of the 

 Territories, and it is so mapped in Hay den's Atlas of Colorado, the reason 

 for this reference being that marine Cretaceous (Fox Hills) fossils were 

 found at various horizons above the coal beds. 4 Others have refeired 

 all of the productive coal measures of this area to the Laramie, 5 basing 

 'their correlation on the stratigraphy, the lithologic character of the beds, 

 and the evidence of the fossil plants. There is no doubt that Fox Hills 



1 Throughout this bulletin the names of fossils are usually changed so as to conform to the nomen- 

 clature adopted in the descriptions that are to follow. Gryphcea newberryi is the l r pper Cretaceous 

 form so frequently referred to in Dr. Newberry's report under the name G ryphcea jntelteri. 



* Op. cit., p. 32. 



s It should be remarked that the molluscau fossils reported by Dr. Newberry from the lower divi- 

 sion seem to belong with the fauna of the overlying shales, and in southern Utah the coal-hearing 

 sandstones at the base of the Cretaceous have yielded fossils that 1 regard as a part of the Colorado 

 fauna. 



4 For detailed sections and descriptions of Cretaceous in southwestern Colorado, see report of W. H. 

 Holmes in Ann. Kept, U. S. Geol. Sur. Terr, for 1873, pp. 242-2G7. 



Tn western Colorado: Reports of A. C Peale, idem, for 1874, pp. 128-155, and for 187G, pp. 170-180; of 

 C. A. White, ibid., pp. 19. 28-34, and other reports in the same series. 



s Lakes, A.: Geology of Colorado coal fields. Ann. Kept. State School of Mines, Denver, 1889, pp. 

 19, 148, 102, etc. 



Hills, R. C: Orographic ami structural features of Rocky mountain geology. Proc. Colo. Sci. Soc 

 vol. in, 1890, p. 380etseq. 



