532 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



Richmondian (Mckles, 1902). The Edenian and Maysvillian faunas 

 represent the return of the Mohawkian faunas, but somewhat changed. 

 In the early Richmondian, however, there was an influx of migrants from 

 a new area, probably the North Atlantic (Anticosti), forming the Rhyn- 

 chotrema capax and R. perlamellosa faunas. 



At the close of the Richmondian all further Cincinnatic records of 

 marine deposits are absent in the interior region. The continent remained 

 emergent for a long time, and when the next short oscillations of the 

 oceans occurred the faunas represented are very different, having several 

 spire-bearing brachiopods and other reminders of the Siluric. The 

 dividing line between the Cincinnatic and Siluric is usually drawn at the 

 top of the Richmondian, but this delimitation will now have to be 

 changed, as it fails to recognize a long interval elsewhere recorded. On 

 Anticosti may be studied a complete section bridging this lost interval, 

 and through 1,134 feet of limestones may be traced the gradual transition 

 of the life of the highest Richmondian into that of the earliest Siluric. 

 The Cincinnatic, therefore, can not be closed with the Richmondian, but 

 must be continued until a considerably later period — one yet to be deter- 

 mined by the Anticosti record. 



NEOPALEOZOIC ERA 



Siluric or Ontario Period 

 See plates 63-71, and pages 489-491 



On the basis of their faunas the American Siluric deposits are geo- 

 graphically divisible into three provinces, the best known being that of 

 the Atlantic realm, which is represented on the continent by three sub- 

 provinces — the Saint Lawrence sea, the Appalachian trough, and the 

 Indiana basin of the Mississippian sea. These waterways also have the 

 longest sequence of formations — in fact, showing a nearly complete rep- 

 resentation of the Siluric system. The next best known province is that 

 of the Hudson sea, whose faunas are of Arctic and northern European 

 derivation. This sea appeared in the United States long after the begin- 

 ning of the Siluric and vanished with the Guelph. The third province 

 is that of the Cordilleran sea, evidently Pacific in origin, but of which 

 little is known. The following synopsis of the crinoids, brachiopods, and 

 trilobites will bring out the relationship of the eastern provinces : 



