60 



THE OPAL SEA 



Pteropod 

 ooze. 



Globioerina 

 and Radio- 

 larian 

 oozes. 



The Red 



Clay. 



bed where, with many millions of others, they 

 help form a " Pteropod ooze." At a depth of, 

 say, two thousand fathoms the same shells of 

 foraminifera are forever raining downward 

 from the surface; but the bottom deposit does 

 not show more than an average of sixty per 

 cent of them. When three thousand fathoms 

 of depth is reached the foraminifera are re- 

 duced to thirty per cent. This decrease is ow- 

 ing to the increased presence of carbonic-acid 

 gas, which, as already suggested, dissolves and 

 destroys the shells. The remainder looks like 

 a gray or blue chalk, is called " Globigerina 

 ooze," and is found chiefly in the North Atlan- 

 tic and Southern oceans. Finally this, too, 

 disappears giving place to a " Eadiolarian 

 ooze," composed of the skeletons of radiolaria 

 or star-shaped organisms less susceptible to the 

 influence of carbonic-acid gas than the foram- 

 inifera. In the greatest depths of all is 

 found the Red Clay or Eed Mud deposits. 



The Eed Clay which covers the deep floors 

 of the Pacific and the Indian oceans is made 

 up of refuse and residue — that which can with- 

 stand the strong chemical action of the gases. 

 In it may be found decomposed volcanic rock, 

 pumice, zeolitic crystals, manganese oxides, 

 meteoric iron, teeth of sharks, and ear bones 



