OCEANIC DEPOSITS AND BOTTOM FAUNA 29 



e.g., the Cape of Good Hope, east coast of Australia, Japan, 

 and the Atlantic coasts of the United States. 



Glauconite is a hydrous double silicate of potassium and 

 trivalent iron (KFeSi 2 O 6 Aq). Its chemical origin is still a 

 mystery. It appears- to result from a metamorphosis of ferru- 

 ginous clay, and since it is most often found within the shells 

 of foraminifera, decomposing organic matter probably plays 

 a part in its formation. It is a mineral belonging to the 

 reducing areas of the deep sea. 



Glauconite is responsible for the withdrawal of potassium 

 from solution in the sea. All submarine muds and clays 

 contain only a small amount, less than i per cent., of 

 potassium. In glauconite areas the fixation of potassium must 

 be considerable, since the purest green sands contain from 7 

 to 8 per cent. In spite of this the addition of potassium to 

 sea-water probably exceeds its withdrawal, and potassium is 

 slowly accumulating in sea-water. 



Glauconite sands are found off the east coast of the United 

 States from Cape Hatteras southward. The collections of the 

 Tuscarora show the sands as present off the coast of California 

 at depths of from 100 to 400 fathoms. 



Pure glauconite sands such as these are, however, rare, 

 the deposits containing, as a rule, remains of calcareous 

 organisms, mineral particles from the continental rocks, and 

 considerable clay. Blue mud has always more clayey matter 

 than the green muds. Green sands and muds are not found in 

 very deep water, between 100 and 900 fathoms being the rule. 

 The Challenger records contain 22 samples of green mud 

 and 7 of green sand. Carbonate of lime is present from mere 

 traces to 56 per cent., the average being 26 per cent. 



Volcanic Muds and Sands occur off those coasts and 

 oceanic islands where volcanic rocks prevail. The volcanic 

 mineral particles are larger in the shallower waters nearer the 

 land, and the deposits are here called volcanic sands. Strictly 

 speaking, volcanic muds are a variety of blue mud. They are 

 light brown, grey, or black in colour, and have an earthy 



