CORRELATIONS 337 



ary plane still higher in the New York series, but I find no suspicion 

 that the plane was put too high till the Hercynian question arose. 



HERCYNIAN FAUNAS EODEVONIAN 



In the recent studies of the Hercynian problem it has been established 

 with a fair degree of certainty that the Hercyn and Erbray faunas are 

 Eodevonian, and in a general way an equivalency is established between 

 these faunas and those of the arenaceous beds of the Gedinnian and 

 Coblenzian, not to go into particulars as to the precise place in these 

 etages to which each belongs. 



It is also fairly well established that the Oriskany fauna at least rep- 

 resents the same stage of faunal evolution and the same general effects 

 upon a considerable number of different genera, which was expressed 

 in Eodevonian time in western Europe. 



IS THE LOWER HELDERBERG EQUIVALENT TO THE HERCYNIAN f 



There is difference of opinion, however, regarding the correlation of 

 the Lower Helderberg fauna with European faunas ; but there appears 

 to be unanimity of opinion among European paleontologists (Kayser, 

 Freeh, Barrois, and others) that while the Lower Helderberg fauna shows 

 affinities with the Hercyn, Erbray, and other faunas of Europe, it is 

 somewhat older; also there seems to be general unanimity of opinion 

 among those discussing the question that the European fauna coming- 

 most nearly to equivalency with the Lower Helderberg of America is the 

 F 2 Konieprussian fauna of Bohemia. 



The real Problems in Determining the Silurian-Devonian 



Boundary for America 



character of the evidence as to transition 



Accepting these determinations as satisfactorily established, how do 

 the facts affect the question as to the boundary plane between the Silu- 

 rian and Devonian systems in North America ? 



It leaves the burden of proof with those who contend that the Lower 

 Helderberg is not in the Silurian ; for it is known to be below the base 

 of the Oriskany, and always below, wherever the Oriskany fauna is 

 known in America. Although several species, and closely allied species, 

 appear to associate the two faunas, the case is clear in America that the 

 passage from Lower Helderberg to Oriskany marks a conspicuous evo- 

 lutional stage in the history of the Paleozoic faunas of North America. 



Furthermore, it is clear that this evolutional stage is clearly marked 

 in western Europe by a similar change in the specific characteristics of 



