252 



REPORT UNITED STATES GEOLOGICAL SURVEY. 



Meek for the Upper Missouri River region constitutes a natural .and 

 reliable basis for the classification of the Cretaceous rocks of much the 

 greater part if not all of the region embracing the Western States and 

 Territories. The mollification of that grouping which is followed in this 

 report consists, as already explained on previous pages, only in omitting 

 certain of the subdivisions which were recognized in the Upper Missouri 

 River region, while the leading features are retained without change. 



These labors have also demonstrated the unity of all the principal 

 brackish-water deposits hitherto known in the Western Territories, and 

 justified their recognition as a comprehensive group of strata under the 

 name of the Laramie Group, which represents a great period in geolog- 

 ical time, and especially such in the geological history of North America. 



The known extent of the vertical range of each species named in the 

 following table, within its own group of strata, has been indicated on pre- 

 Aious pages in the notes that follow each list of the fossils which were 

 collected at the localities visited during the season. Their geographical 

 distribution is indicated by columns in the table which represent certain 

 arbitrarily designated regions embracing the whole extent of my season's 

 travels, to which is added for comparison a column representing the 

 Upper Missouri River region. 



Table showing the geographical distribution of the Cretaceous species collected during the sea- 

 son of 1877. 



FOX HILLS GEOUP. 





Caryophyllia egcria White 



Lingula nitida Meek & Hayden 



Ostrea patina Meek & Hayden 



Ostrea soleniscus Meek 



Ostrea coalvillcnsis Meek 



Ostrea congesta Conrad 



Ostrea (Alectryonia) sannionis White 



Placunopsis hilliardensis White 



Pteria haydeni Hall & Meek 



Ptcria linguiformis Evans & Shumard 



Pteria gc.strodcs Meek 



Pteria (Pseudoptera) fibrosa Meek & Hayden 



Pteria (Pseudoptera) rhytophora Meek 



Pteria {Pseudoptera) propleura Mock 



Pteria ( Oxytoma) nebrascana Evans & Shumard 



Pinna lakesi White 



Inoceramus barabini Morton 



Inoceramus howelli White 



Inoceramus crccius Meek 



Inoceramus oblongus Meek 



Inoceramus vanuxemi Meek & Hayden 



Inoceramus pertenuis Meek & Hayden 



Inoceramus problcmaticus Schlotheim 



Volsella (Brachydontes) multilinigera Meek 



Crenella elegantula Meek & Hayden 



Nucula planimarginata Meek & Hayden 



Nucula canccllata Meek & Hayden 



Barbatia coalvillensis White 



Sphceriola ? obliqua Meek 



Sphcsriola 1 endotrachys Meek 



Tancredia amcricana Meek & Hayden 



Tancredia ? coelionotus White 



Teniella humilis Meek & Hayden 



Cardium. speciosum Meek & Hayden 



Cardium curtum Meek&Hayden 



Cardium subcurtum Meek 



Cardium trite. White 



Protocardia rara Evans & Shumard ' 



