wHirE.1 CRETACEOUS FOSSILS FROM WHITE RIVER VALLEY. 225 



2i:Cardimn speciosnm Meek & Hajden. 



This species has not been found so common west of the Roclcy ]\Touut- 

 ains as east of them. Besides tliis locality, I also found it at tliat of 

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

 ap])ears to possess all the characteristics of the tyi^ical examples. Its 

 l)resence here, associiited as it is Avith the next following species, indi- 

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



3. Mactra {Cijmhopliora) alta Meek & Hayden. 



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

 in any other than the ui)permost strata of the Fox Hills Group. It is, 

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

 which is also indicated by the position of the strata in relation to thost> 

 (if tlie Laramie Group. For remarks on this and the two i^receding 

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

 ix, U. S. Geol. Siu-. Terr. 



4. Anisomijon centrdle Meek. 



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

 might A^dth e(pial pro]iriety be referred to some one of those which Mr. 

 Meek has described fiom the Upper Missouri Eiver region, all of whicn 

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

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

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



5. Aetccon icoosteri White. 



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

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

 found only in Southern and Eastern Colorado. 



(». BacuUtes ovatus Say. 



It has already been shoAvn 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 

 jis especially characterizing its highest fossiliferous horizon. 



These Danlbrth 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 jdace in consequence of movements 

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

 continuousuess of sedimentation. 



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

 for the year 187G, all relating to it, except matters of a paleontological 

 (jharacter, will be omitted fi'om this report. Proceeding down the valley 

 ()f White IlivQT a few comparatively unimportant collections v^ere made 

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

 lX)int to point between Piiion liidge and Haven Park, where the upper 

 strata of that group were found exposed in the vaUey of White Eiver. 

 The fossils collected were not abundant, and consisted of oidy Hve spe- 

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

 Groui) at other localities. 

 15 G s 



