544 C. SCHUCHERT— PALEOGEOGRAPHY OF XORTH AMERICA 



Oriskanian. — In the eastern region of the Appalachian trough, from 

 Maryland to southern New York, the Helderbergian appears to pass with- 

 out break into the Oriskanian. The faunas are still of the southern 

 Atlantic type and are unknown in other areas. Gradually they change 

 into the typical Oriskany element, characterized by Hipparionyx proxi- 

 mus, Spirifer murcliisoni, and Rensselceria ovoides. These pertain to a 

 northern invasion, also well known in the Saint Lawrence sea at many 

 localities. Clarke has termed it the Coblenzian invasion, because of its 

 relationship to this northern European Lower Devonic series. While it 

 is well developed in the Saint Lawrence trough, the best American devel- 

 opment occurs in the Grand Greve limestone, where the longest sequence 

 of Paleodevonic formations in America is found. 



On the west side of the Cincinnati axis a very different late Oriskanian 

 biota is preserved in the Camden, which extends from southwestern Illi- 

 nois throughout western Tennessee. This, the Amphigenia fauna, has 

 many characters in common with the Msecuru of Brazil, and forms the 

 introductory one to the later Onondaga. 



In the Cordilleran sea Oriskanian faunas are unknown, though some 

 deposits there are regarded as probably belonging to this time. 



Eiian. — In eastern North America there were two distinct subprovinces 

 of the Middle Devonic that, at different times were variously interblended. 

 The Gulf invasion, first seen in the Camden of late Oriskanian time, con- 

 tinued unbroken into the Onondaga or Jeffersonville in southwestern Illi- 

 nois. This was the southern element that introduced the widespread De- 

 vonic coral faunas, and as the invasion extended around the northern 

 region of the Cincinnati axis, it blended with the other invasion from the 

 North Atlantic. The latter represented the Oriskanian- Schoharie element, 

 and together with the southern invasion furnished the later Onondaga or 

 early Erian faunas that spread as far north as James basin. West of the 

 Indiana basin there are no deposits of this time except in the Great Basin 

 of Nevada. Walcott has described the latter in his volume on the Eureka 

 district, but the species need revision to accord with present knowledge. 

 To the writer, the Great Basin and the Mississippian sea appear to have 

 almost nothing in common. 



Before the close of the Onondaga the intercommunication between the 

 New York basin and the Saint Lawrence sea was permanently destroyed. 

 Subsequently the Appalachian sea intermittently received migrations 

 from the middle Atlantic through the New Jersey straits. These addi- 

 tions are most noticeable during the Hamilton, Tully, Ithaca, and Che- 

 mung. Every now and then the TropidoJeptus carinatus fauna of the 

 Atlantic swarmed into this trough, but did not make much progress in 



