54 PROCEEDINGS OF THE NATIONAL MUSEUM vol.76 



trilobites of eastern North Ameri^^a and in a more recent paper by 

 the same author and Willard on Chazyan brachiopods in Tennessee 

 and Virginia. 



The need of studying the papers on Appalachian brachiopods by 

 Eaymond and Willard arose only since the completion of the present 

 work. The new species described and others identified in these 

 papers attain the respectable total of 73 species. It is to be noted 

 also that the species have been discriminated with uncommon atten- 

 tion to external details of shell structure. Still it is evident that 

 their collections from the Chazyan deposits in the southern Appa- 

 lachian Valley and those from the Stones River limestones in cen- 

 tral Tennessee are far inferior, both as regards quantity and quality, 

 to those accumulated in the National Museum by me and my asso- 

 ciates. With more and better material probably neither Raymond 

 nor Willard would have identified so many of the Virginia and 

 Tennessee species with Champlain Valley Chazyan and Mississippi 

 Valley Stones River and Black River species. It seems probable 

 also that they would have found that some of the identified or sup- 

 posedly closely allied species are even only doubtfully assignable 

 to the same genera. But my strongest criticism of both the brach- 

 iopod and the preceding trilobite paper concerns the stratigraphic 

 assignments of many of the species. I have studied and collected 

 from all the Virginia and Tenessee localities mentioned in these 

 papers and therefore am prepared to say that many of the asserted 

 occurrences of strictly the same species in two or more of the Chazyan 

 formations are based on mistaken identifications of beds. Indeed, 

 these stratigraphic inaccuracies are so numerous that they very seri- 

 ously impair the validity of Raymond's conclusions "* regarding the 

 relationships of the Chazyan fossils of Tennessee and Virginia. 



Cause of difficulties in correlating Ewopean and American 

 Ordovician formations. — Aside from erroneous or merely loose iden- 

 tifications of fossils and misunderstandings, the main cause of our 

 troubles in this connection lies in the indisputable fact that we are 

 dealing with successive and slowly modifying aspects of the gen- 

 erally very different faunas of particular oceanic realms that at times 

 invaded European epicontinental basins and at the same or, more 

 probably, at other times invaded inlets to Appalachian troughs on 

 the western side of the sea. Under the belief that these invasions 

 occurred mostly at alternating intervals on the two sides of the 

 Atlantic — in other words, when emergent conditions were prevailing 

 on the other side — it follows that the sequence of beds and faunas 

 in any one of the areas in which deposits of Ordovician waters that 

 invaded from, say, the Middle Atlantic sea occur can represent only 



2* Raymond, P. E., Mus. Comp. Zool. Bull., vol. 70, pp. 300-309, 1928. 



