PERMANENCE 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 lived. 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 way 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, was little by little confined to 
