white.! CEOW CREEK. 163 



tlie strata in which, they occur. But this subject will' be discussed 

 farther on in this report, in connection with facts of a similar nature in 

 relation to other species also. 



Going westwardly from the fossil and coal locality, in the neighbor- 

 hood of Maynard's ranch, I passed the base of the foot-hills and went a 

 few miles up "Box Elder Canon," examining the strata of the different 

 Mesozoic formations as they successively rise from beneath the Laramie 

 Group and each other, and are upturned there against the flanks of the 

 mountains. 



Owing to the friable condition of all the Laramie strata, they have 

 been mostly removed by erosion wherever they were formerly upturned. 

 The formations that successively rise beneath these are, in the descend- 

 ing order, the Fox Hills, Colorado, and Dakota Groups, of Cretaceous 

 age, and the " Bed Beds," of supposed Triassic age, the latter resting 

 directly upon the granite. In this vicinity I failed to find any fossils in 

 any of the strata of these formations beneath the Laramie Group, but 

 from the well-known litkologieal characteristics of each group respect- 

 ively, they were readily identified. The strata of the Fox Hills and Col- 

 orado Groups, at least the upper portion of the latter, being like those 

 of the Laramie Group, comparatively soft and easily eroded, the surface 

 of the plains is continuous toward the mountains over these formations, 

 the foot-hills of the mountains being composed mainly of the harder 

 strata of the Dakota Group and the Bed Beds. The lower portion of the 

 Colorado Group is composed in this region of light-colored, firm, siliceous 

 shales, which in some places are rocky enough to form hog-backs of con- 

 siderable elevation. At no locality east of the mountains did I find the 

 strata of the Colorado Group composed of the soft, blue, clayey shales 

 that so generally characterize that group west of the mountains. In the 

 last-named region, however, the lower portion of the Colorado Group is 

 almost everywhere characterized by a greater or less thickness of bluish 

 or dark fissile shales, which is perhaps only a modification of the more 

 rocky portion, holding a similar position in the group east of the mount- 

 ains. 



From Box Elder Canon I traversed the space between that point and 

 Cache a la Poudre Biver, a tributary of the South Platte, which I reached 

 opposite the town of Greeley, going by the way of Higley's coal-mine. 

 I recognized the existence of the Laramie Group beneath the surface 

 debris all the way, but collected no fossils on that portion of my route. 

 From the valley of the Cache a la Poudre I proceeded eastward to the 

 valley of Crow Creek, another tributary of the South Platte, having its 

 confluence with that river a few miles below that of the Cache a la Poudre. 

 Upon the elevated ground, constituting the watershed between these 

 two tributaries, some .five or six miles northeastward from Greeley, I 

 found some slight exposures of strata, among which I recognized the 

 fossiliferous horizon of the neighborhood of Maynard's ranch. Here I 

 obtained not only the Ostrea and Anomia which I collected there, but 

 also Corbula subundata Meek andHayden, and Corbicula clebumi White. 

 Going directly to Crow Creek to camp, I commenced an examination of 

 the valley- I found no exposures of strata between that point and the 

 mouth of the creek, a distance of about five miles, but along the eastern 

 summit of the valley side, where I hoped to have found exposures, the 

 surface was found to be largely occupied by sand dunes. Proceeding 

 up the valley I found no exposures of strata for five miles more, nor 

 until I reached a point about ten miles from the mouth of the creek. 

 From this point to five or six miles farther up the valley I found numer- 

 ous limited exposures of strata containing many fossils, mainly on the 



