OOZES 221 



clayey matter coloured by the oxides of iron and man- 

 ganese. This deposit varies greatly in composition both 

 with respect to the species of organisms present and 

 their relative abundance, and also in the abundance and 

 nature of the mineral constituents. In all the great 

 depths of the ocean, exceeding 2,500 or 3,000 fathoms, 

 Globigerina Ooze gives place to Red Clay, even in 

 those regions where pelagic Foraminifera inhabit the 

 surface waters in great profusion ; this is ascribed to 

 the longer time during which the shells are exposed 

 to the solvent action of sea water, while falling through 

 the greater depth of water, and while lying uncovered 

 on the bottom. 



Globigerina Ooze is estimated to cover an area of 

 about 49,520,000 square miles (or 128,824,000 square 

 kilometres) — i.e., about 22,500,000 square miles in the 

 Atlantic Ocean, about 14,800,000 square miles in the 

 Pacific Ocean, and about 12,220,000 square miles in 

 the Indian Ocean. 



5. Pteropod Ooze. — This deposit differs from Globi- 

 gerina Ooze only in the greater abundance of the 

 shells of pelagic Molluscs (Pteropods and Heteropods), 

 and occurs characteristically at lesser depths than the 

 Globigerina Ooze (Fig. 164). Thus Pteropod Ooze may 

 be said to attain its typical development at depths of 

 800 to 1,000 fathoms, while Globigerina Ooze occurs 

 typically at depths of 1,500 to 2,000 fathoms. The 

 reason why the shells of pelagic Molluscs are removed 

 from the deposits at lesser depths than the shells of 

 pelagic Foraminifera is believed to be that these thin 

 and fragile shells present a larger surface to the solvent 

 action of sea water. 



Pteropod Ooze is estimated to cover an area of 

 about 400,000 square miles (or 1,000,000 square 

 kilometres), principally in the Atlantic Ocean. 



