XII. 



SUBMARINE DEPOSITS. 



The explorations of the "Blake" during my stay on board 

 did not extend to oceanic basins far from land, but were limited 

 to the investiofation of enclosed seas like the Caribbean and Gulf 

 of Mexico, and of the continental edges of a part of the west- 

 ern basin of the North Atlantic. The " Blake " subsequently 

 sounded the oceanic basin to the west of the Bermudas and 

 north of the Windward Islands. I have myself had no oppor- 

 tunity of seeing on the spot the deposits characteristic of a true 

 oceanic area, and have supplemented the results of the " Blake " 

 by those obtained by the " Challenger " and " Tuscarora " in 

 the great oceanic basins. 



The character of the bottom specimens near shore differs very 

 materially from that of deposits brought from corresponding- 

 depths in the open ocean. Along the Atlantic shores of the 

 United States, these deposits are primarily affected by the geo- 

 logical structure of the mainland, the width of the continental 

 shelf, the direction of the currents and of the prevailing winds, 

 and the presence or absence of rivers. Within the Caribbean 

 and on the oceanic face of the Greater and Lesser Antilles, the 

 presence of an equatorial current, of the tradewinds, of volcanic 

 rocks, and of extensive limestone plateaux, introduces conditions 

 which differ radically from those operating upon the Atlantic 

 coast. In the Gulf of Mexico, although the distance from shore 

 of the central part of the basin is often very considerable, still 

 the character of the bottom deposits is always somewhat affected 

 by its peculiar physical conditions. And nowhere in the Gulf 

 or the Caribbean, or around the Atlantic slope of the United 

 States, do we find any ooze strictly comparable to that of the 

 open oceanic basins. 



