200 



SKETCHES OF CREATION. 



Black Seas of the Old "World. Indeed, the area covered 

 by this shallow expanse of deserted and isolated sea-water 

 was the Lectonia of the New World, which, like the level 

 region in the south of Russia, once overflowed by the high- 

 er waters of the great seas which stretch along the confines 



Fig. 77. Outlines of the North American Continent at the end of Mesozoic Time. 



The existing boundaries are indicated by dotted lines, 

 a, a, a. The great Tertiary Sea, stretching from the Arctic Ocean, along the eastern 



flanks of the Rocky Mountains, to Texas, b, b. The great " Central Plateau," in 



modern times a worn-out continental area. 



of the two continents, was destined to be gradually drained. 

 The drainage in both cases was effected partly by the up- 

 raising of the continent, and partly by the bursting of bar- 

 riers and deepening of channels at the point where the im- 

 prisoned waters were escaping. But, while the drainage 



