OCEANIC DEPOSITS AND BOTTOM FAUNA 37 



The I'elagic Deposits are divided into five main types : 



1. Pteropod Ooze is found in the shallower waters, far 

 from continental land, on tropical and subtropical ridges, and 

 comes especially within the coral reef regions where warm 

 water with small annual variation is found at the surface. It 

 consists mainly of shells of pteropods and heteropods. Al- 

 though these mollusca are found practically everywhere in the 

 surface waters of tropical and subtropical regions, their dead 

 shells are absent in the deeper deposits. A few traces are met 

 with down as low as 2,000 fathoms. The Challenger lists 

 comprise thirteen samples, only one of which is from over 

 1,500 fathoms deep. 



Pteropod ooze was only found by the Challenger in the 

 Atlantic, where it occurs near the Azores, the Antilles, west of 

 the Canaries, and on the South Atlantic median ridge between 

 Ascension and Tristan da Cunha. This ooze has also been 

 found by other expeditions in the Indian (by the Valdivia) 

 and Pacific Oceans. 



The total area is small, not exceeding 0*4 per cent, of the 

 ocean floor. The percentage of carbonate of lime is, of course, 

 high, averaging 80 per cent. 



2. Globigerina Ooze forms 29-2 per cent, of the ocean floor. 

 The average depth of the ocean is about 2,000 fathoms, and 

 this ooze is the most widely distributed on these average depths. 

 It is made up largely of the dead shells of surface foraminifera, 

 the genus globigerina predominating. 



Globigerina ooze was originally obtained by the cable 

 steamers in the North Atlantic, w r here it was first collected by 

 Lieutenant Berryman of the U.S. Navy, and described by 

 Ehrenberg and Bailey in 1853. These foraminifera occur also 

 in other deposits, the term "globigerina ooze" being restricted 

 to those which contain over 30 per cent, of carbonate of lime, 

 mainly made up of the dead shells of foraminifera. The 

 majority of the surface living foraminifera, from whose shells 

 this deposit is mainly derived, live in warm tropical waters. 



The colour of the ooze is white, yellowish, or greyish, 



