2O2 



The Realm of Nature 



CHAP. 



gently-rounded contour of the ocean-beds is largely due. 

 MM. Murray and Renard in their report on the deposits 

 collected during the Challenger expedition have adopted 

 the following classification : 



MARINE DEPOSITS 



i. Deep-Sea Deposits 



(beyond I oof at horns}. 



I. PELAGIC DEPOSITS, 

 formed in deep water 

 remote from land. 



II. TERRIGENOUS DE- 

 POSITS, formed in 

 deep and shallow 

 water close to land 



Red Clay 

 Radiolarian Ooze 

 Diatom Ooze 

 Globigerina Ooze 

 Pteropod Ooze 



Blue Mud 

 Red Mud 

 Green Mud 

 Volcanic Mud 

 Coral Mud 



2. Shallow- Water Deposits (in less than 

 100 fathoms}, sands, gravels, muds, etc. 



3. Littoral Deposits (betiveen high and 

 low water marks}, sands, gravels, muds, 

 etc. 



269. Terrigenous Deposits. Sediment, such as fine 

 clayey mud, requires a very long time to settle to the bottom 

 of fresh and still more of running water, but in sea-water, 

 especially when the temperature is high, it settles out much 

 more rapidly. The smaller a particle of mud and the 

 deeper the sea, the farther from land will the particle be 

 carried by currents before it falls to the bottom. As a rule, 

 however, land-derived material all reaches the bed of the 

 ocean within 100 or 200 miles of the shore ; only in excep- 

 tional circumstances does it extend to a greater distance 

 than 300 miles. The line of 250 miles from the coast 

 shown on Plate XII. is practically the boundary of terri- 

 genous deposits. Very large and swift muddy rivers like 

 the Congo and Amazon ( 230) form such exceptions. 

 Congo mud has been found 600 miles from shore. The 

 Arabian Sea and Bay of Bengal are carpeted for nearly 

 1000 miles from land by the mud of the Indus and Ganges 

 river systems. Other exceptions result from icebergs, 



