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 tlie 

 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 pelagic 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 calcare- 

 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- 



