178 STUDIES IN INSECT LIFE, ETC. 



3. DIATOM-OOZE consists of the small flinty 

 skeletons of plants. Diatoms are unicellular 

 lowly algae ; but lowly though they be, they are 

 the ultimate food which keeps the inhabitants 

 of the ocean going. Without diatoms there 

 would be no marine fauna. It is estimated that 

 these delicate and microscopic shells cover an 

 area of nearly 11,000,000 square miles of the 

 bottom of the sea, chiefly in the Southern Seas. 



4. GLOBIGERINA-OOZE is a pallid, somewhat 

 sticky, yellowish-grey, semi-liquid mud formed 

 of the chalky skeletons of unicellular animals 

 which swarm in the upper waters and never reach 

 the deeper depths of the ocean, since they are 

 dissolved if exposed too long a time to the action 

 of salt water. But the bottom of the Atlantic 

 is seldom more than 2,000 fathoms from the 

 surface and forms " the great grey level plains 

 of ooze " previously referred to. The great bulk 

 of the Atlantic is floored by these skeletons, and 

 Sir John Murray estimated that they cover an 

 area of practically 50,000,000 square miles, in 

 all oceans. 



5. PTEROPOD-OOZE. A much smaller deposit is 

 the Pteropod-ooze, which consists of a floor of 

 shells of surface-living molluscs. This covers an 



