162 REPOET UNITED STATES GEOLOGICAL SUEVEY. 



openings in tlie coal-bed have been made in a broad depression of the 

 surface, or shallow valley, along a line a couple of miles in length and 

 having a northerly and southerly trend. The rocks here, and in this 

 vicinity, both of the Laramie and Fox Hills Groui)S, consist of soft 

 sandstones and sandy shales, the latter apx)arently predominating, and 

 among the strata of ihe Laramie Group there are occasional layers that 

 contain a considerable amount of carbonaceous matter, besides the bed 

 of coal before referred to. 



In this neighborhood the only fossils obtained were from the Laramie 

 Group, and with the exception of a single imperfect example of a Gorbula 

 probably C. jyerundata Meek and Hayden, they belong to one species 

 each of Ostrea and Anomia. The latter is the Anpmia micronema of Meek 

 which is common but not abundant. The Ostrea was found to be quite 

 abundant, especially in some places. They were found to occupy at 

 least two layers of considerable constancy and extent and only a few 

 feet apart. Tlie principal oyster layer is between 50 and 100 feet above 

 the bed of coal already mentioned. The position of the coal and the 

 fossiliferous layers in relation to either the l3ase or summit of the Lara- 

 mie Grouj) as it exists in this region could not be ascertained, but obser- 

 vations made both here and in the valley of Crow Creek, where the same 

 layers were clearly recognized, seem to indicate that their i)osition is 

 nearer to the base than to the summit of the group as it is developed 

 east of the Eocky Mountains. It may be remarked here in passing that 

 the aggregate thickness of the Laramie Grouj) is much less east of the 

 mountains in Colorado than it is west of them in the great basin of Green 

 Eiver. 



The shells of Ostrea found at the locality near Maynard's Eanch, like 

 those of all the known sioecies of that genus proper, are very variable, 

 so much so that it would be impossible to represent the species (for I 

 regard them as belonging to one species only) by the most careful selec- 

 tion of only a few examples. After a careful study of a large collection 

 of these shells, made not only at this locality, but also in numerous other 

 localities of the Laramie strata of this region east of the mountains, 

 most of which are from substantially one and the same limited horizon, I 

 am convinced that they constitute only one species, notwithstanding 

 their" great variation. A large proportion of the lighter, thinner, and 

 more elongate shells, are i^lainly identical with those forms that were 

 ^originally described by Meek and Hayden as Ostrea glabra, their exam- 

 ples having been obtained from the Judith Eiver beds of the Upper 

 Missouri Eiver region. Others, among the larger aud more massive 

 shells, are undistinguishable from 0. ivyomingensis Meek, as found at 

 the typical locality at Point of Eocks Station, IJnion Pacilic Eailroad, in 

 the valley of Bitter Creek, Wyoming. There are still others, small 

 examples, that may reasonably he referred to those forms which Meek, 

 in vol. ix of the IJnited States Geological Survey of the Territories 

 referred, and perhaps correctly, to 0. subtrigonalis Evans & Shumard. 

 Among the large collections of these shells that I have made in the region 

 adjacent to the eastern base of the Eocky Mountains in Colorado, it is 

 easy to select forms that will connect together all three of those that have 

 just been mentioned, and which have been described as distinct species. 

 Such selections and arrangement leave the differences between any of 

 the varietal forms so employed far within the most rigid limits of recog- 

 nized specific variation among the Ostreidcv. If this conclusion is correct, 

 as it is belicA^ed to be, it not ouly shows an identity of three forms, hitli- 

 erto supposed to be specifically distinct, but it also shows a very wide 

 geograi^hical distribution of the species, and a geological equivalency of 



