224 THE SEA FLOOR 



B. Terrigenous Deposits. 



6. Blue Mud. This deposit is the one most fre- 

 quently met with in the deeper waters surrounding 

 continental land and in enclosed and partially en- 

 closed seas. It is principally composed of materials 

 derived from the disintegration of continental land, 

 consisting largely of the fragments and minerals 

 of continental rocks (the older crystalline and schisto- 

 crystalline rocks, quartzites, sandstones and lime- 

 stones) of various dimensions, but usually larger near 

 shore and smaller as the deep sea is approached, 

 except in the regions affected by floating ice. Quartz 

 is the characteristic mineral species, associated with 

 orthoclase and plagioclase felspars, green hornblende, 

 mica, etc ; glauconite is usually present, but not in 

 such abundance as in the Green Mud. There is usually 

 a considerable proportion of amorphous clayey matter, 

 increasing in amount with increasing distance from 

 land, so that some of the deeper samples have a 

 decidedly clayey aspect, but the deposit, as a rule, 

 may be described as earthy rather than clayey. In some 

 situations the remains of bottom-living organisms may 

 be present in considerable numbers, and in others the 

 remains of pelagic organisms may be so abundant that 

 the deposit resembles a Globigerina Ooze. 



Blue Mud is estimated to cover an area of about 

 14,500,000 square miles (or 37,700,000 square kilo- 

 metres). 



7. Red Mud. 1 This is a local variety of Blue Mud, 

 hitherto known only from the Yellow Sea in the 

 Pacific, and off the Brazilian coast in the Atlantic, 

 characterized by the presence of a large quantity of 

 reddish ferruginous matter brought down by the large 

 rivers in the vicinity. 



