136 THREE CRUISES OF THE “ BLAKE." 
hundred fathoms, then a very gentle descent to the edge of the 
sharp, steep slope forming the outer eastern edge of the Blake 
Plateau, at a depth of nearly six hundred fathoms. 
It is interesting to speculate how this peculiar profile, so dif- 
ferent from that of any other part of our coast, was formed. 
The explanation to my mind is comparatively simple. The pre- 
sent outer eastern edge of the Blake Plateau, which is now at a 
depth of six hundred fathoms, was at one time at a much higher 
level. In fact, I assume that this slope probably represents the 
remnant of the slope formed at the time when it began at the 
hundred-fathom line, and that this trough with unequal sides has 
been worn away by the action of the Gulf Stream acting upon 
the Blake Plateau from a geological time which we can trace 
with a certain degree of accuracy. 
We may also imagine the slope off the Carolinas and Georgia 
to be due, not to the wearing action of the Gulf Stream along 
the surface of the ancient continental plateau, but to the depo- 
sition of a large amount of silt from the remains of pelagie ani- 
mals, which has gradually formed the bank — the Blake Plateau 
— occupying the angle between the northern extremity of the 
Bahama Bank and Cape Hatteras. 
In the one case, the hundred-fathom line existed formerly far 
out to sea beyond its present position, along a line now repre- 
sented by about the five-hundred-fathom line ; in the other case, 
the hundred-fathom line was nearer the coast, perhaps even 
within the present shore. The accumulated growth of caleare- 
ous animals together with the deposition of pelagic material has 
gradually enlarged the outer edge of the former continental pla- 
teau, and thus the distinct line of demarcation usually formed 
by the hundred-fathom line has been obliterated along that por- 
tion of our coast. To this may be due the formation of the 
Blake Plateau. 
In other words, the old continental line extended at least two 
hundred and fifty to three hundred miles farther to the east- 
ward, forming a huge plateau, the hundred-fathom line of which 
was found where the six-hundred-fathom line now runs, and 
stretched so far south as to include the Bahamas and Cuba in 
this great submarine plateau. The elevation of the Blake Pla- 
