86 



LARAMIE FLORA OF THE DENVER BASIN. 



group in the valley of South Platte Biver to the base of 

 the Monument Creek group on Cherry Creek Plateau, is 

 estimated at about 1,800 feet. So far as I could discover, 

 only about the lower 200 or 250 feet of this series is known 

 to contain invertebrate fossils; and the lower 700 or 800 

 feet appears also to contain all the coal of the Laramie 

 group in this region. 



This area was visited by T. W. Stanton and 

 me in 1896, 98 and the thickest section found 

 showed the invertebrates and plants through a 

 distance of only 40 or 50 feet. The beds under- 

 lying the Laramie were at no place disclosed. 



In this connection inquiry was made of Prof. 

 Junius Henderson, of the University of Colo- 

 rado, who is known to have an extensive knowl- 

 edge of the geology of northeastern Colorado. 

 In a letter to me Prof. Henderson states that 

 after a very thorough exploration of this region 

 he has not been able to fix the thickness of the 

 Laramie section in this area with any, degree 

 of positiveness. He says: "On the whole I 

 have no evidence that would show more than 

 100 feet of Laramie around Crow Creek, but 

 my impression is that it is a little more." 



It appears to have been thought by those 

 who had previously visited this area that there 

 was probably a considerable thickness of 

 Laramie beds both beneath and above the 

 Crow Creek exposures and, further, that these 

 exposures should hold a position relatively high 

 in the full Laramie section, as would naturally 

 be, inferred from their location far out on the 

 plains and away from the mountains against 

 which the Laramie is so steeply upturned. 

 This view also finds some confirmation in the 

 fact that only one of the species of inverte- 

 brates {Ostrea glabra) common on Crow Creek 

 is known to occur in the Laramie of the Denver 

 Basin. This was the view at first entertained 

 by Prof. Henderson, but he states that his 

 faith in the high position of the deposits on 

 Crow Creek was shaken by the "finding of Fox 

 Hills strata in geographically high positions on 

 the divides and in the ravines far out from the 

 mountains and in some instances unquestion- 

 ably not far below fossiliferous beds of the 

 Laramie." 



Continuing; he says : 



In the irregular cross-bedded sandstone on top of Wild- 

 cat Mound northwest of Platteville, within 40 feet of the 

 Fox Hills sandstone, I found a thick bed containing 



» Stanton, T. W., and Knowlton, F. H., Stratigraphy and'paleon- 

 tology of the Laramie and related formations in Wyoming: Geol. Soo. 

 America Bull., vol. 8, p. 151, 1897. 



great quantities of Ostrea glabra, with a few specimens 

 which I have identified as Corbicula cleburni White, C. 

 fracta Meek, C. micropistha White, and Anomia micro- 

 nema. They were not very well preserved, but cer- 

 tainly they are correctly determined generically and I 

 believe also specifically. The shales intervening between 

 this stratum and the topmost sandstone of the Fox Hills 

 is doubtless the same as that found between the Fox 

 Hills and the coal beds at Windsor and elsewhere, but I 

 have never been able to find any determinative fossils 

 or ascertain whether or not it is marine. At Wildcat 

 Mound Halymenites major occurs in both the marine and 

 the Corbicula beds. 



Going northward from Wildcat' Mound to Milliken the 

 upper Fox Hills sandstone thins out very much and is 

 overlain by shales. From 100 to 150 feet up in the shale 

 is a coal vein, but no fossils were found in this shale. 



I also failed to find the Ostrea-Corbicula sandstone at 

 Windsor, where the exposure of the strata overlying the 

 uppermost sandstone of the Fox Hills is almost complete 

 for a long distance, or at Indian Spring mine, north of 

 Wellington, where such a sandstone if present would show 

 in the slope between this sandstone and the coal. 



Throughout the Crow Creek district, eastward to Wild- 

 cat Creek and Cottonwood Spring, I always found Cor- 

 biculas, etc., in contact with or beneath the lowest coal. 

 On the divide some miles east of Crow Creek, near Grease- 

 wood Lake, southeast of Osgood post office, I found Fox 

 Hills strata yielding Lunatia, Tellina, Cardium, Denta- 

 lium, Mactra, Nucula, Baroda, and Halymenites. Almost 

 anywhere to the east, west, northeast, and north of Os- 

 good Ostrea glabra and various species of Corbicula may 

 be found, with coal seams, some of the fossiliferous beds 

 being surely not many feet above the marine Fox Hills 

 strata just mentioned. 



At Cottonwood Springs, some 15 miles northeast of 

 Orchard, I found a 4-foot bed of shale containing Ostrea 

 glabra, Anomia micronema, Corbicula cleburni, C. fracta, 

 Corbula subtrigonalis, and Melania wyomingensis. Thirty 

 feet of shales immediately underlying this bed yielded 

 Nucula, Baroda, Cardium specioswm, and Turritellaf 



I found Fox Hills strata again well up the west valley 

 slope of Wildcat Creek, north of Fort Morgan. There I 

 found Vaniella humilis and Pholadomya subventricosa, 

 which usually are found at the base of and below the 

 uppermost Fox Hills sandstone, together with Tellina 

 scitula and Lucina sp. I found Fox Hills marine fossils 

 in the bluffs and slopes of the South Platte Valley as far 

 out as Canton, Weldon, and Messex. 



From all the evidence now at hand I can not see how 

 the lowest fossil horizon at Crow Creek can be, at most, 

 more than 50 to 100 feet above the Fox Hills marine 

 strata. 



A critical analysis of the geographic and 

 stratigraphic range of these Crow Creek inver- 

 tebrates would be of considerable interest, but 

 this is outside of my knowledge or the scope of 

 the present report. I may simply note in pass- 

 ing that it appears to have been demonstrated, 

 that certain of the species present at Crow 

 Creek have a very considerable vertical range, 



