wmTE.l CROW CREEK. 163 



the strata in "wliicli tliey occiu*. But this subject will be discussed 

 fartlier on in tliis rei^ort, in connection with facts of a similar nature in 

 relation to other species also. 



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

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

 few miles u[) " Box Elder Canon," examining the strata of the diflereut 

 Mesozoic formations as they successively rise from beneath the Laramie 

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

 mountains. 



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

 been mostly removed by erosion wherever they were formerly uptui-ned. 

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

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

 age, and the " Eed 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 lithological characteristics of each group respect- 

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

 orado Groups, at least the upi)er portion of the latter, being like those 

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

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

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

 strata of the Dakota Grouj) and the Eed Beds. The lower portion of the 

 Colorado Group is comi)Osed 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 comjiosed 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 i^osition in the group east of the mount- 

 ains. 



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

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

 opj)osite 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 Poutb-e I proceeded eastward to the 

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

 continence with that river a few miles below that of the Cache L 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 exiiosiu-es 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 Corbida suhundata Meek and Hayden, and Corhicula clebiuiii White. 

 Going directly to Crow Creek to camj), 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 

 siunmit of the valley side, v/here I hoped to have found exposm-es, the 

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

 up the valley I foiuid 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 fiirthcr up the valley I found nimier- 

 ous limited exi^osures of strata containing many fossils, mainly on the 



