MUDS, AND SANDS 225 



Red Mud is estimated to cover an area of about 

 100,000 square miles (or 260,000 square kilometres). 



8. Green Mud. — This is a variety of Blue Mud, 

 found along bold exposed coasts where no very large 

 rivers enter the sea, and distinguished by the greater 

 or less abundance of green glauconite grains and 

 glauconitic casts (internal models in green sand), of 

 the shells of calcareous organisms, usually associated 

 with a greenish amorphous (probably organic) matter. 

 In the shallower depths the glauconitic grains and 

 casts are sometimes associated with phosphatic con- 

 cretions, while the amorphous clayey matter is less 

 abundant, and the deposits, being more granular and 

 more incoherent, are called Green Sands. 



Green Mud is estimated to cover an area of about 

 1,000,000 square miles (or 2,600,000 square kilo- 

 metres) . 



9. Volcanic Mud. — This deposit occurs around 

 oceanic islands and submarine elevations of volcanic 

 origin, and is made up largely of volcanic rock frag- 

 ments and volcanic mineral particles, such as lapilli 

 of basaltic and andesitic rocks, especially the vitreous 

 varieties, sanidine, plagioclase, augite, hornblende, 

 rhombic pyroxenes, olivine, and magnetite. In the 

 shallower waters the volcanic particles are larger, 

 associated with less amorphous clayey matter, and the 

 deposits, being less coherent, are called Volcanic 

 Sands. The remains of floating or bottom-living 

 calcareous organisms may become so abundant that 

 it is sometimes difficult to distinguish this deposit 

 from a Globigerina Ooze on the one hand, or from a 

 Coral Mud or Sand on the other. 



Volcanic Mud is estimated to cover an area of 

 about 750,000 square miles (or 1,950,000 square kilo- 

 metres). 



15 



