PERMAXENCE OF CONTINENTS AND OCEANIC BASINS. 137 



teau probably dates back to the end of the cretaceous period, 

 the time when the plateau of Mexico was raised, by which what- 

 ever communication may have existed between the waters of the 

 Atlantic and those of the Pacific was cut off, and there were 

 formed a number of islands, more or less extensive, in the range 

 of the Greater or Lesser Antilles. 



We may attempt from the topography of the bottom of the 

 Gulf of Mexico, of the Straits of Florida, and of the ocean off' 

 the east coast of the Southern States, to reconstruct the ancient 

 course of the Gulf Stream from the time of the cretaceous, and 

 to speculate upon its action in modifying the topography of the 

 continental shelf which runs from the Bahamas to Cape Hat- 

 teras. 



At that time the Gulf Stream, passing between Yucatan, then 

 a submarine plateau of comparatively moderate depth, and Cuba, 

 furrowed the deep channel, one thousand fathoms or more, which 

 now separates Yucatan from Cuba. The Gulf Stream then lost 

 itself northward in a Mississippi bay, and spread fan-shaped 

 partly over the submarine plateau of Florida. It brought, how- 

 ever, an accession of materials, by the deposition of which the 

 plateaux of Yucatan and of Florida were slowly built up, and 

 which also supplied food to the innumerable marine animals 

 whose former existence is proved by the structure of the very 

 plateau upon which they must have Hved. The Gulf Stream 

 thus contracted its own boundaries, and was forced into the 

 narrower channel it had constructed between Yucatan and 

 Cuba. As a consequence, it cut an ever deepening trough, and 

 in proportion as Florida rose from the sea it was also compelled 

 to find an outlet for the mass of water by which the Florida 

 peninsula had been covered. It naturally followed the track 

 of least resistance, and forced its w^ay up-hill over the lowest 

 part of the plateau, the southern point of Florida, through the 

 then comparatively shallow passage of the Straits of Bemini, 

 which it must have deepened by degrees as Florida was build- 

 ing up. 



The mass of water which in the early part of the tertiary 

 period forced its way north, partly up the Mississippi, and partly 

 east over the peninsula of Florida, w^as little by little confined to 



