MUDS AND GREEN SAND 1 75 



(1) Blue Mud. — The materials of this deposit, which are 

 principally, though not altogether, derived from the land, are very 

 heterogeneous. Quartz grains in an excessively fine state of sub- 

 division are very abundant ; clay is often a considerable ingredient, 

 and then the mud is plastic when wet, but it is usually more earthy 

 than clay-like. Minute particles of other terrigenous minerals, like 

 felspar, hornblende, augite, etc., are common. CaC0 3 is almost 

 always present, averaging 7 %, and in some instances rising to 

 25 °/o ', this is due chiefly to the foraminiferal shells, both of those 

 species which live at the surface and those which live on the bottom. 

 Siliceous organisms are also present to the average amount of 3 %, 

 and are principally diatoms, radiolarians, and spicules of sponges. 

 (ilauconite_ is found in nearly all the samples. The blue colour 

 of this mud is due to the sulphide of iron, and the organic matter 

 which prevents the oxidation of the sulphide. Of the terrigenous 

 deep-sea deposits blue mud is the most extensively developed; 

 it is estimated as covering 14,500,000 square miles of the sea- 

 bottom, and surrounds almost all coasts, and fills enclosed basins 

 like the Mediterranean and even the Arctic Ocean. The depths 

 at which blue mud is found range from 125 to 2800 fathoms. 



(2) Red Mud is a local development, which occurs principally 

 upon the Atlantic coast of Brazil, and in the Yellow Sea of China. 

 Silt of this character, the red colour of which is due to Fe 2 3 , is 

 brought down in large quantities by the Amazon and the Orinoco. 

 Foraminiferal shells are abundant ; radiolarians very rare. 



(3) Green Mud is much the same in character as the blue 

 mud, but owes its green colour to the higher percentage of glauco- 

 nite which it contains. 



(4) Green Sand is granular in appearance, and is made up 

 largely of grains of glauconite and casts in that material of the 

 interior of foraminiferal shells, together with nearly 50% of CaC0 3 . 

 The green sands occur in shallower water than the muds, and often 

 within the 100-fathom line, as in the case of a deposit of this kind 

 which is now forming off the coast of Georgia and the Carolinas. 

 The estimated area of the green muds and sands is 1,000,000 

 square miles. 



