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 (KFeSigOgAq). Its chemical origin is still a 

 mystery. It appears to resuit 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 minerai belonging to the 

 reducing areas of the deep sea. 



Glauconite is responsible for the withdrawal of potassium 

 from solution in the sea. AU 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 considérable, 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 Flatteras southward. The collections of the 

 Tuscarora show the sands as présent ofif the coast of California 

 at depths of from 100 to 400 fathoms. 



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

 the deposits containing, as a rule, remains of calcareous 

 organisms, minerai particles from the continental rocks, and 

 considérable 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 présent from mère 

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



Volcaiiic Muds and Sands occur ofif those coasts and 

 oceanic islands where volcanic rocks prevail. The volcanic 

 minerai particles are larger in the shallower waters nearer the 

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

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

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



