316 



PALEOZOIC TIME CARBONIFEROUS AGE. 



tain some fossils that ally the Fauna more with the European than with 

 that of the Interior Continental basin of North America. Among them are 



Fi2. 549. 



Tracks of Sauropus primgevus (X \ 



the Spirifer glaber (fig. 554) and Productus Martini, both of which are European 

 species. 



III. General Observations. 



Geography. — As in the first half of the Upper Silurian there 

 was a period — the Niagara — when a sea profuse in life, and thereby- 

 making limestones, covered a large part of the Interior Continental 

 basin ; and again in the early part of the Devonian age — the 

 Upper Helderberg period — the same conditions were repeated ; 

 so in the early Carboniferous there was a similar clear and open 

 mediterranean sea, and limestones were forming from the relics of 

 its abundant population. In the period of the Upper Silurian 

 referred to, the living species were of a miscellaneous character, 

 Brachiopods, Crinoids, and Corals occurring in nearly equal pro- 

 portions ; but in that of the Devonian, Corals were greatly predo- 

 minant, and in that of the Carboniferous, Crinoids had as remark- 

 able a pre-eminence. By an open sea is meant one having free 

 connection in some part with the ocean ; and this connection must 

 have been on the south, towards the Mexican Gulf; for the arena- 

 ceous deposits of the wide Appalachian region show that there was 

 not, probably, a direct opening eastward into the Atlantic. The 

 mediterranean sea alluded to was, in fact, only an extension north- 

 ward of the Mexican Gulf. 



These interior waters in the Subcarboniferous period had nar- 

 rowed limits on the east ; for they no longer spread over New York, 



