258 PHYSICAL GEOLOGY 



and even mud, find permanent lodgment in sheltered bays, and 

 off low coasts where wave action is weak. On the other hand, 

 coarse material may extend far out from shore, provided the 

 water is shallow and the waves are strong. Most of the sand 

 is deposited beyond the gravel, while beyond the sand fine 

 muds are spread over the ocean floor to the limit of sediments 

 brought by streams from the land. 



Blue mud is the most extensive land-derived deposit, and 

 is estimated to cover over 14,000,000 square miles of the sea 

 bottom (nearly five times the area of the United States). It 

 commonly contains tiny particles of numerous minerals, and 

 is blue because the organic matter present prevents the oxida- 

 tion of the iron. Red mud occurs over relatively small areas; 

 here the clay contained so much Fe 2 3 when brought to the 

 sea that it has been only partially deoxidized. Green mud 

 and greensand occur over an area equal to about one third 

 that of the United States, and owe their color to the relatively 

 large amount of the mineral glauconite present. Glauconite 

 is a complex mineral containing alumina, potash, and iron. 

 Extensive deposits of greensand now form part of the coastal 

 plain of New Jersey. 



ORGANIC DEPOSITS AND RED CLAY 



Organic deposits are composed not of materials derived 

 directly from the land, but principally of materials that were 

 brought in solution by rivers to the sea, taken from 

 solution in the sea water by plants or animals and built into 

 their shells or other hard parts, and deposited upon the ocean 

 bottom at the death of these organisms. 



Oozes. This term is applied to fine oceanic muds of or- 

 ganic origin. The various oozes are named from the organisms 

 whose remains contributed most to the deposit. Often, how- 

 ever, the leading constituent of an ooze makes up only 20 

 or 30 per cent of the total deposit. Globigerina ooze 

 (Fig. 277) is a calcareous deposit which takes its name from a 



