94 EXPEDITION OF THE CHALLENGER&quot; m 



Foraminifera and other calcareous shelled organ 

 isms, the indications of life become scanty at 

 depths beyond 500 or 600 fathoms, while almost 

 all traces of it disappear at greater depths, and at 

 1,000 to 2,000 fathoms the bottom is covered with 

 a fine clay. 



Dr. Carpenter has discussed the significance of 

 this remarkable fact, and he is disposed to attri 

 bute the absence of life at great depths, partly 

 to the absence of any circulation of the water of 

 the Mediterranean at such depths, and partly to 

 the exhaustion of the oxygen of the water by the 

 organic matter contained in the fine clay, which 

 he conceives to be formed by the finest particles 

 of the mud brought down by the rivers which 

 flow into the Mediterranean. 



However this may be, the explanation thus 

 offered of the presence of the fine mud, and of the 

 absence of organisms which ordinarily live at the 

 bottom, does not account for the absence of 

 the skeletons of the organisms which undoubtedly 

 abound at the surface of the Mediterranean ; and 

 it would seem to have no application to the re 

 markable fact discovered by the Challenger, that 

 in the open Atlantic and Pacific Oceans, in the 

 midst of the great intermediate zone, and 

 thousands of miles away from the embouchure of 

 any river, the sea-bottom, at depths approaching 

 to and beyond 3,000 fathoms, no longer consists of 

 Globigcrina ooze, but of an excessively fine red clay. 



