MARINE DEPOSITS 205 



and especially where cold and warm currents 

 meet in the overlying surface water. 



4. Volcanic Mud. — This type occurs around 

 the oceanic islands of volcanic formation and 

 along coasts where there are outcrops of 

 volcanic rocks, the chief characteristic being 

 the relative abundance of volcanic rock frag- 

 ments and mineral particles. In the shallower 

 waters near shore the deposits are coarser and 

 contain less fine clayey matter, and are there- 

 fore called Volcanic Sands. 



5. Coral Mud. — This deposit is found around 

 the oceanic islands of coral formation and 

 along coasts bordered by coral reefs, being 

 characterised by the abundance of fragments 

 of corals and other calcareous organisms living 

 in the shallow waters and on the reefs. These 

 fragments form a coarse sand or gravel near 

 the reefs, and the deposit is then called Coral 

 Sand, but with increasing depth and distance 

 from the reefs the calcareous materials from 

 the reefs become finer and finer in grain, 

 forming frequently an impalpable coral mud, 

 which passes at its seaward margin into 

 pteropod or globigerina ooze. 



Pelagic Deposits 



6. Globigerina Ooze. — This type of deposit 

 is second in importance only to the red clay, 

 covering an extensive area throughout all the 



