496 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



sion that the modification was accomplished in transit between the conti- 

 nents or before the invasion of the latter, rather than within the median 

 continental seas themselves. As to the expansional evolution within these 

 interior seas, it seems to me this was never the important factor in the 

 evolution of marine faunas that it is believed to be by Chamberlin and 

 other recent writers, none of whom has made a specialty of the study of 

 fossil faunas. 



The Burlington crinoid fauna and the bryozoan and other faunas in 

 the Maysville formations about Cincinnati afford perhaps as good ex- 

 amples of Paleozoic expansional evolution as can be cited. But even in 

 these cases we may well inquire if it is not rather a matter of favorable 

 habitat and preservation, or even more of exceptional opportunity and 

 effort to make full collections than of prolific evolution ? Certainly a very 

 strong nucleus of the Burlington crinoid fauna existed in the preceding 

 Kinderhook and Fern Glen faunas, while the lower Maysville fauna is 

 merely a later phase of the late Trenton Catheys fauna which invaded the 

 same regions long before. In the latter case the change most certainly 

 did not take place within the continental seas, since the fauna is almost 

 entirely absent in the otherwise highly fossiliferous intervening forma- 

 tions. 



The apparently local faunal distinctions which probably suggested the 

 idea of expansional evolution in geologic times, as, for instance, the dif- 

 ference in the Niagaran faunas in Wisconsin, N"ew York, and Tennessee, 

 or in the middle Ordovician faunas in the same three States, are due to 

 other causes than merely local peculiarities in development of contem- 

 poraneous faunas. As shown in discussing the "early Trenton'^ deposits 

 and faunas (pages 367-373) and those of the Magaran (pages 558-561), 

 these differences are due chiefly to the fact that the several faunas in- 

 vaded the continents from different oceanic basins, the Wisconsin faunas 

 in question being of Arctic origin, the Tennessee faunas came in from 

 the Gulf of Mexico, and the N'ew York in part from the Atlantic. More- 

 over, most of these contrasted faunal expressions, which have been sup- 

 posed to be contemporaneous, are in fact not of the same ages in the three 

 areas. These facts, of course, weaken the argument very materially, if 

 indeed they do not completely vitiate it. 



Another belief that helped in framing the suggestion of expansional 

 evolution is that great intermingling of previously distinct faunas oc- 

 curred at times of exceptional submergence of continents. However, 

 detailed analysis of the faunas, on which this belief is chiefly based, 

 proves, as is briefly outlined in preceding parts of this work (pages 370 

 and 494), that commonly the supposition is quite groundless. As shown, 



