292 THREE CRUISES OF THE " BLAKE." 



derstaud 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 

 alonof 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 it 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 larof'e 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 volcanic 

 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. Its 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 httle to the westward of the Bermudas. There seems to be a 

 triangular-shaped basin filled with red clay to the eastward of 



^ 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. 



