292 THREE CRUISES OF THE “ BLAKE.’ 
derstand how perfectly sea-urchins or mollusks would be pre- 
served in this homogeneous substance, and gradually compressed 
into solid white chalk. 
Commander Bartlett observed that the strong current passing 
over the ridge of the Windward Passage between Cuba and 
San Domingo swept it entirely clean, so that but little animal 
life was found to live upon it. But immediately beyond this, 
on the Caribbean side, the mud and silt are deposited in great 
quantities, and animal life becomes plentiful again. This, as I 
have already stated, was also our experience while dredging 
along the so-called axis of the Gulf Stream. The bottom of 
that region, swept clean by the Stream, forms a great contrast 
to the slope off Hatteras, where the silt accumulates in such 
masses as to make 1t often difficult to detach the shot of the 
sounding-wire when it has sunk deep into it. These and similar 
deposits, accumulating within restricted areas, may often guide 
us in determining the direction of currents, and the distribution 
of pelagic types may also assist us in defining the slower move- 
ments of large masses of water. 
The red clay deposit first discovered by the “ Challenger ” is 
found at depths greater than two thousand fathoms, and is 
probably in part the result of the decomposition of voleanic 
products. The materials of the red clay are present in all de- 
posits, but at lesser depths its presence is obscured by the 
more rapid accumulation of calcareous matter. Near shore, 
and upon our continental shelf or near its base, even at very 
considerable depths,! we do not find the characteristic red clay 
deposit of the deeper basins of the Atlantic. Tts presence is 
hidden by the larger mass of continental detritus, of volcanic 
muds and sands, of globigerina ooze, and of other calcareous 
deep-water deposits. 
According to the “ Challenger,” red clay has not been found 
in the western basin of the North Atlantic except at one locality 
a little to the westward of the Bermudas. There seems to be a 
triangular-shaped basin filled with red clay to the eastward of 
1 This has been the experience of both which genuine red clay was brought up 
the * Blake ” and of the U. S. Fish Com- by the *Challenger? in more favored 
mission, when dredging at depths from localities. 
