THE WORK OF THE OCEAN 



327 



Deep-sea deposits beyond 

 100 fathoms... 



2. Shallow-water deposits 

 between low- water mark 

 and 100 fathoms 



3. Littoral deposits between 

 high- and low-water marks 



Red clay 

 Radiolarian ooze 

 Diatom ooze 

 Globigerina ooze 

 Pteropod ooze 

 Blue mud 

 Red mud 

 Green mud 

 Volcanic mud 

 Coral mud 



\ Sands, gravels, 

 / muds. etc. 



( Sands, gravels, 

 I muds, etc. 



1 I. Pelagic 



deposits 



formed in deep 

 water , removed 

 from land 



II. Terrigenous depos- 

 its formed in deep 

 and shallow water, 

 mostly close to 

 land 



In spite of this classification of Murray, the coral and volcanic 

 muds cannot be regarded as terrigenous, and shells, coral, etc., are 

 found abundantly in shallow-water deposits. It is to be noted 

 that the pelagic deposits are partly inorganic and partly organic 

 in origin. The inorganic materials may be of mechanical or chem- 

 ical origin. 



Mechanical inorganic deposits. The mechanical deposits of the 

 deep sea come (1) from the land by the ordinary processes of grada- 

 tion, (2) from volcanic vents, and (3) from extra-terrestrial sources. 

 The terrigenous materials which reach the deep sea are, as a rule, 

 only the finest products of land decay, and are carried out by move- 

 ments of water and by winds. They are not commonly recognized 

 in the dredgings more than 200 miles from shore, but opposite the 

 mouths of great rivers they extend much farther, 1,000 miles 

 in the case of the Amazon. They are especially abundant on the 

 slopes of the continental shelves, where the blue, green, and red muds 

 are associated with volcanic and coral muds. The color of these 

 various muds depends in part on the changes they have undergone 

 since their deposition. The green muds usually contain enough 

 glauconite to give them their color, and are most commonly found 

 off bold coasts where sedimentation is not rapid. The blue muds 

 indicate lack of oxidation, or perhaps deoxidation. Red muds are 

 not common, though found in some situations. These deposits 

 are analogous, in a general way, to certain shales, marls, etc., found 

 on the continents. 



