24 A TEXTBOOK OF OCEANOGRAPHY 



1. Littoral (derived from land de- f Shore deposits (3 above). 



nudation) I Continental shelf deposits (2 above). 



2. Hemipeiagic (partly of land, partly \ , 



t> \ i I -tJ 3DOVC. 



of marine origin) J 



i A. above. The red clay and radio- 



3. Eitpclagic (of marine and cosmic J larian ooze being distinguished as 

 origin) I abyssal, the remainder as epi- 



l lophic. 



The former classification is followed in this book. 



Littoral Deposits. 



The littoral deposits (in the narrower sense), as defined by 

 Murray and Renard, include those between high and low 

 water marks. As defined by continental writers, the littoral 

 deposits include those of the continental shelf as well. In the 

 former sense the littoral deposits are estimated to cover 62,500 

 square miles of the earth's surface. They consist essentially 

 of boulders, gravels, and sands, though mud is by no means 

 unknown in sheltered bays and estuaries. Their nature is 

 determined by the local features of the adjoining land. There 

 is almost an infinite variety of the littoral deposits, from huge 

 boulders resulting from the denudation of cliffs to fine mud. 



The seaward limit in the British Isles is often marked by a 

 growth of seaweed known as Laminaria. 



The littoral zone is the habitat of a large number and variety 

 of organisms, these naturally varying from the mangrove 

 swamps and coral reefs of the tropics to the shell-fish beds of 

 temperate regions. Generally speaking, the animal life is 

 abundant, the chief groups represented being the Mollusca 

 (cockles, mussels), Crustacea (crabs), Echinoids (sea urchins 

 and starfish), and worms. Some of these organisms are of 

 economic importance, giving rise to extensive "fisheries" 

 e.g., for mussels, cockles, periwinkles, and clams (in the 

 U.S.A.). 



The Shallow-Water Deposits. 



These are met with from low-water mark to the loo-fathom 

 line. According to Murray and Renard, they cover about 



