252 



EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



Meek for the Upper Missouri Eiver 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 modification of that grouping which is followed in this 

 report consists, as already explained on i^revious pages, only in omitting 

 certain of the subdivisions which were recognized in the Upper Missouri 

 Eiver 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- 

 vious 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 Avhich 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 Eiver region. 



Taile allowing the geograpMcal distribution of the Cretaceous species collected during the sea- 

 son of 1877. 



rOX HILLS GROUP. 



m o 



a 'So 



1. Caryophyllia egeria WTiite 



2. lAngula nitida Meek & Hayden 



3. Ostrca patina Meek & Hayden 



4. Ostrea soleniscus Meek. 



5. Ostrea coalvillensis Meek 



6. Ostrea eongesta Conrad 



7. Ostrea (Alectryonia) .sannionis White 



8 Placunopsis hilliardensis White 



9. Pteria haydeni SaR & Mesk 



10. Fteria linguiformis Evans & SImmard 



11. Pteria gastrodes Meek 



12. Pteria (Pseiidoptera) fibrosa Meek & Hayden 



13. Pteria (Pseudoptera.) rhytophora Meek 



14. Pteria (Pseudoptera) propleura Mock 



15. Pteria (Oxytoma) nebrascana Evans & Shmnard. 

 10. Pinna lalcesi White 



17. Inoceramus barabini Morton 



18. Inoceramus howelli White 



19. Inoceramus erectus M.cq]s. 



20. Inoceramus oblongus Meek 



21. Inoceramus vanuzemi Meek & Hayden 



22. Inoceramus pertcnuis Meek & Hayden 



23. Inoceranfius problematicus Schlotheim 



24. Yolsella (Brachydontcs) multilinig era Meek 



25. Crenella elegantula Meek & Hayden 



2G. Nucula planimarginata Meek & Hayden 



27. Nucula cancellata Meek & Hayden 



28. Barbatia coalvillensis Wliite 



29. Sphceriola ? obliqua Mcelc 



30. Sphceriola 1 endotrachys Meek 



31. Tancredia americana Meek & Hayden 



S2. Tancredia ? coelionotus White . 



33. Veniella humilis Meek & Hayden , 



34. Gardium, speciosum Meek & Hayden , 



35. Gardium, curtum Meelt & Hayden , 



30. Gardium subcurtum Meek 



37. Gardium triti'- White 



38. Protocardia rara Evans & Shumard 



