THK DISTRIBUTION OF ANIMALS 



445 



with substances derived from the wearing- away of the land by 

 the action of the waves and tides, with the sand, mud, and other 

 substances brought down to the sea by rivers, and with the 

 skeletal remains of many animals. All of these substances are 

 spoken of as terrigenous deposits. Beyond this the ocean bed 

 is covered for a considerable distance with deposits which con- 

 sist largely of calcium carbonate, often as much as 90 per cent, 

 and this is due to the presence of the shells of many minute 

 animals, which live at the surface of the sea and as they die 

 their skeletons fall to the bottom. In the shallower regions 

 these deposits are called pteropod ooze, since they consist largely 

 of the shells of the Pteropoda ; in deeper waters the shells of 

 certain Protozoa predominate, and there we have the character- 

 istic grayish globigerina ooze, which extends to depths of 4000 

 or 5000 meters. Passing into still deeper waters, we rind no 

 trace of shells of calcium carbonate ; they have all been dis- 

 solved. Instead we may find siliceous deposits, due chiefly to 

 the siliceous shells of the minute plants called diatoms, and 

 hence these deposits are spoken of as diatom ooze ; this ooze, so 

 far as we know at present, is confined to the southern ocean, 

 a little north of the Antarctic Circle. Further, in the deepest 

 portions of the western and central Pacific is found a radiolarian 

 ooze, consisting of the shells of the Radiolaria, and hence sili- 

 ceous. But the greater portion of the deep-sea basin beyond 

 the region of the globigerina ooze is covered with the so-called 

 red clay deposit, which varies in composition, but is composed 

 chiefly of fragments of volcanic material. Sharks' teeth and 

 some very hard bones of vertebrates have been found in this 

 red clay, often inclosed in nodules of manganese or iron. 



The temperature of the ocean is an important factor in the 

 distribution of animal life ; there we find no such range of tem- 

 perature as there is on land. The highest temperature at the 

 surface of the ocean is about 32 C. (89 F.), the lowest about 

 — i° C. (30 F.), thus giving a range of less than 34° C. (6o° F. ), 

 while on land man has been subjected to a temperature 

 49° C. (120 F.) in the desert and of -6i° C. (-78 F.) in 

 Arctic regions, a range of about 1 10° C. (200 F.). It has been 

 determined that the heat of the sun does not penetrate to 

 depth of more than 300 meters; then the temperature falls 



