white.] CRETACEOUS FOSSILS FROM WHITE EIVER VALLEY. 225 



2. Cardium speciosum Meek & Hayden. 



This species lias not been found so common west of the Eocky Mount- 

 ains as east of them. Besides this locality, I also found it at that of 

 Dodds's Ranch, presently to be noticed. In these western localities it 

 appears to possess all the characteristics of the typical examples. Its 

 presence here, associated as it is with the next following species, indi- 

 cates that the strata containing it are the uppermost of the series. 



3. Mactra (Cymbophora) alta Meek & Hayden. 



So far as I am aware, no example of this species has ever been found 

 in any other than the uppermost strata of the Fox Hills Group. It is, 

 therefore, valuable here as indicating the highest horizon of the group ; 

 winch is also indicated by the position of the strata in relation to thosa 

 of the Laramie Group. For remarks on this and the two j)receding 

 species, see foregoing pages; and for figures and descriptions, see vol. 

 ix. U. S. Geol. Sur. Terr." 



4. Anisomyon centrale Meek. 



The examples found here seem to be referable to this species, but they 

 might with equal propriety be referred to some one of those which Mr. 

 Meek has described from the Upper Missouri River region, all of whicn 

 are difficult of separation. Anisomyon appears to range higher in the Fox 

 Hills Group west of the Rocky Mountains than east of them. I have 

 never before found it associated with either of the two foregoing species. 



5. Actccon woostcri White. 



A single fragment was found, associated with the fossils of the fore- 

 going fist, that seems to belong to this species, which has been hitherto 

 found only in Southern and Eastern Colorado. 



t>. Baculites ovatus Say. 



It has already been shown that this species is not known to range to 

 the top of the Fox Hills Group in the Upper Missouri River region, nor in 

 Eastern Colorado. Here, however, it is not only found in the uppermost 

 strata of that group, but it is associated with species that are regarded 

 as especially characterizing its highest fossiliferous horizon. 



These Danforth Hills localities are especially interesting, because they 

 contain, in one and the same exposure of strata, fossiliferous horizons that 

 are respectively characteristic of the Fox Hills and Laramie Groups 

 within comparatively a few feet of each other, and with no unconformity 

 of strata between them. It seems, therefore, conclusive that the change 

 from a marine to a brackish condition of the waters, and the consequent 

 total change of aqueous fauna, took place in consequence of movements 

 that occiuTed elsewhere, but which were not sufficient here to break the 

 continuousness of sedimentation. 



The structural geology of this region having been reported on by me 

 for the year 1876, all relating to it, except matters of a paleontological 

 character, will be omitted from this report. Proceeding down the valley 

 of White River a few comparatively unimportant collections were made 

 on the way. The first of these was made from Wasatch strata from 

 point to point between Piiion Ridge and Raven Park, where the upper 

 strata of that group were found exposed in the valley of White River. 

 The fossils collected were not abundant, and consisted of only five spe- 

 cies, most or all of which are known to pass up into the Green River 

 Group at other localities. 



15 g s 



