v] ANCIENT GEOGRAPHY 79 



be opened anywhere. Lastly, just as it is impossible 

 to make a political world-map of, say, the 19th century, 

 it is futile to chart a geological epoch. We might as 

 well attempt to fit in one picture a series of super- 

 imposed dissolving views. 



The evidence for reconstructions is direct and 

 circumstantial. Marine fossils indicate sea, terrestrial 

 fossils land at the respective time. In North America 

 occurred a void gap of land-vertebrates during the 

 Jurassic epoch, but towards its close came in a rich 

 fauna of Dinosaurs, tortoises and mammals of sorts 

 known to have existed long before in Europe. 

 Between Alaska and Canada came in the most 

 specialised Ichthyosaurs and Plesiosaurs, closely re- 

 lated to those of the European seas, showing that 

 there must have existed seaway from Europe to the 

 north of Greenland, whilst Canada-Greenland-Europe 

 formed a barrier to marines but a bridge to terrestrials. 

 Then, during the upper Cretaceous North America 

 was severed into an eastern and a western half, so that 

 the gulf-fauna could mix with another from the polar 

 sea. 



There is obvious affinity between the faunas of 

 South America and Africa, besides groups which 

 probably have got there from a common North 

 American-European centre. Some of the circum- 

 stantial evidence for a direct South American- African 

 connexion is as follows : 



