1902.J AND ANCIENT GEOGRAPHY. 358 



exist, and was not brought about until the mutual relations had gone 

 through various and entirely different stages. 



a. North America. 



If we want to get an idea of the configuration of North America 

 during Mesozoic times, we have to consult in the first line Neu- 

 mayr's well-known map (1890). According to this, in the Jurassic, 

 the northern and eastern parts of North America formed a conti- 

 nental mass, which extended well to the west (Utah peninsula), 

 while the northwest was covered by the sea that separated America 

 from Northeastern Asia. At the same time this continent (Nearc- 

 tic) was bounded by sea to the south, Mexico and the West Indies 

 being submerged. 1 This representation, however, needs correction, 

 chiefly as regards the West Indies, as we have seen above. 



Differing but little from the view taken by Neumayr is that of 

 Koken (1893, pi* T ) Wltn respect to the Lower Cretaceous period; 

 but here the land extends considerably to the northwest and 

 includes parts of Mexico, a conception which is also to be modi- 

 fied, as we shall presently see. 



The general history of North America during the Cretaceous 

 period is best represented by Dana (1895, pp. 813, 874, 881). 

 According to him, Western North America was largely land during 

 the Lower Cretaceous and continuous with the rest. In the Upper 

 Cretaceous, however, chiefly in its earlier part, a central depression 

 became evident, which extended from the south (Gulf of Mexico) 

 northward and possibly reached the Arctic Ocean, dividing the 

 continent into an eastern and a western half. The western half, as 

 we have seen above (p. 318), became connected across Bering Sea 

 with Asia at about this time. 2 At the end of the Cretaceous 

 (Laramie) and in the beginning of the Tertiary an extended eleva- 

 tion began, which culminated in the formation of the Rocky Moun- 

 tains, and by this process the interior Cretaceous sea became land 

 again, which resulted in the reconnection of Western and Eastern 

 North America. But, although there was a geographical union, 

 Eastern and Western North America remained separated bionomi- 



1 Compare, also, Logan, W. N., in Jonrn. of Geology, Vol. 8, 1900, but here 

 the Jurassic ocean of the Northwest is considerably reduced in size and repre- 

 sented only by a shallow bay. 



2 Temporarily the Cretaceous sea of the interior was connected in British Co- 

 lumbia with the Pacific (see Kossmat, 1895, p. 474). 



