138 THREE CRUISES OF THE “ BLAKE.” 
the single channel of the Straits of Bemini, and then the whole 
mass of the Gulf Stream flowed northward over the shallow 
Blake Plateau extending north of the Bahamas to Cape Hat- 
teras. It is this part of the Blake Plateau which, if I am right 
in tracing its past history, has been worn away by the unceas- 
ing flow of the Gulf Stream. 
The Gulf Stream now flows north of the Straits of Bemini 
upon this comparatively shallow submarine Blake Plateau, with 
an average depth of about four hundred and fifty fathoms, and 
finally pours into the deep water of the Atlantie over the edge 
of the steep slope south of Cape Hatteras. At the same time it 
precipitates on this slope all the silt it has carried on its bottom, 
accumulated mainly through the decay of pelagic material and 
the wearing action of the Gulf Stream in its course northward. 
A similar action, but on a smaller scale, also takes place on the 
steep western and northeastern slopes of the Yucatan Bank. 
The shallow surface waters of a part of the Stream pour over 
this bank, and deposit on its slopes the silt held in suspension, 
and whatever materials are gathered along its course by its 
action upon the smaller banks and reefs of the great bank 
itself. 
We have, unfortunately, no very definite data regarding the 
wearing action of water so densely charged with silt as is shown 
by the immense quantity deposited by "the Gulf Stream on the 
northeastern edge of the Blake Plateau, just south of Cape 
Hatteras. The Mississippi, with a depth of say five fathoms, 
and a velocity not much greater than that of the Gulf Stream, 
has in a couple of years dug out a depth of at least eighty feet 
a short distance back of its bar. What may be the wearing ac- 
tion of a mighty river like the Gulf Stream, having an average 
depth of three hundred and fifty fathoms, and a breadth of some 
fifty to seventy-five miles, with a velocity of five miles, it is diffi- 
cult to say. Supposing, however, that this wearing action is 
no greater than the aerial denudation over the area of the Mis- 
sissippi drainage basin, — that is, at the rate of one foot in six 
thousand years, and it certainly is not too much to assume the 
1 The different shades on the map (see Fig. 176) correspond with the respective 
velocities of 1, 2, 3, 4, and 5 knots per hour. 
