MUSEUM OF COMPAExlTIVE ZOOLOGY. 75 



probably represents the remnant of the slope formed at the time when 

 it began at the 100 fathom line, and that this trough with unequal 

 sides has been worn away by the action of the Gulf Stream, wearing 

 away the Blake plateau from a geological time which we can trace 

 with a considerable degree of accuracy. 



In other words, the old continental line extended at least 250 to 

 300 miles farther to the eastward, forming a huge plateau, the 100 

 fathom line of which extended to where the GOO fathom line now runs, 

 and probably stretched so far south as to include the Bahamas and 

 Cuba in this great submarine plateau. The elevation of the Blake 

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

 time when tlie plateau of Mexico was raised, thus cutting off what- 

 ever communication may have existed between the waters of the At- 

 lantic and those of the Pacific, forming at the same time a number 

 of islands, more or less extensive, in the range of the Larger and Lesser 

 Antilles. 



At that time, the Gulf Stream passing between Yucatan, then a sub- 

 marine plateau of comparatively moderate depth, and Cuba, furrowed 

 the deep channel, 1,000 fathoms or more, which now separates Yuca- 

 tan from Cuba. The Gulf Stream then lost itself northward in the 

 great Mississippi Bay, and extended fan-shaped in part over the subma- 

 rine plateau of Florida. It brought, however, an accession of materials 

 by the deposition of which the plateaus of Yucatan and of Florida were 

 gradually built up, and which also supplied food to the innumerable 

 marine animals whose existence is proved by the geological 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 conse- 

 quence, 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 

 tlie then comparatively shallow passage of the Straits of Bernini, 

 which the Gulf Stream must have deepened by degrees as Florida was 

 rising. 



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

 forced its way north partly up the Mississippi, and east over the penin- 

 sula of Florida, was little by little confined to the single channel of the 

 Straits of Bernini, and the whole mass of the Gulf Stream then flowed 



