NORTH AMERICA AND THEIR VERTEBRATE FAUNA. IS3 



in Nova Scotia, and on page 1018, in a map of the Thuringien, shows an arm 

 of the sea reaching across from north of England to Nova Scotia."" 



Koken (Festband der Neues Jahrbuch fur Mineralogie, Geologic u. 

 Paleontologie, 1907, p. 525) says that the Zechstein deposits of Nova Scotia 

 {thelocalitj oiSchizodus and Aucella mentioned above) are outlying deposits of 

 the Arctic Ocean. De Lapparent (according to Koken) would have the deposit 

 connected with the Paleozoic Mediterranean (see the map of the Thuringien 

 cited above) , but this is not borne out by the fauna. There is a possibility, 

 despite the lack of connecting sediments, that it was connected with the 

 western American province. The decision must be made in the future. We may 

 still be certain, in any case, of the presence of a North American-Greenland- 

 North Etiropean land-mass. 



From the foregoing citations it is apparent that the site of the North 

 Atlantic Ocean was occupied in pre-Permian time by a great land-mass. The 

 condition of the land in the Permian is uncertain, but there were possibly 

 some breaks across it, as the Davis Strait, which would constitute a barrier 

 to migrations between Europe and North America. 



On the eastern land-mass the Hercynian chain completed its develop- 

 ment before the Permian time, was eroded, and re-elevated in the Permian. 

 On the western land, the Appalachian Mountains were not elevated until 

 the later part of the Permian. If, as is probable, the Appalachians were 

 elevated by a great world movement which was manifest earlier in Europe 

 as the Hercynian chain (Armorican-Variscan) and progressed toward the 

 west, it is probable that the North Atlantic continent carried the connecting 

 link in the late Carboniferous and Permian. The ends of the links are seen 

 in the rias coasts of Great Britain, France, and Newfoundland. That no 

 remnants of the mountains are found by soundings in the North Atlantic is 

 not surprising, for even if the great basin was formed in Mesozoic time, the 

 previous exposure was sufficiently long to wear the mountains down to low 

 altitude. Witness the reduction of the Appalachians to a peneplain condi- 

 tion by Jurassic or early Cretaceous time. 



Either a break in the North Atlantic continent or the presence of high 

 mountains would have been an efficient barrier to the migrations of the 

 Permo-Carboniferous reptiles and amphibians, and either or both of these 

 geographic features occurred in late Carboniferous or Permian time, on the 

 land connection between Europe and North America, permitting the migra- 

 tion of the earlier Carboniferous or Permo-Carboniferous forms and isolating 

 the later and more specialized forms. 



The possibility of migration was again established in the Triassic, as 

 shown by an abundance of common forms. 



The possible connection with South America has been suggested by 

 Broom, who believes that somewhere in that continent the common ancestors 



» The author has been unable to trace the origin of the statement of De Lapparent. It may be taken 

 from Geinitz, K. Leopold, CaroUn. Acad., Bd. 33, i866.' 



