MUSEUM OF COMPARATIVE 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 600 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 the 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 
the then comparatively shallow passage of the Straits of Bemini, 
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 Bemini, and the whole mass of the Gulf Stream then flowed 
