380 



GEOLOGY. 



1. 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^ 

 muds, etc. 



I. Pelagic deposits 

 formed in deep 

 water removed 

 from land. 



II. Terrigenous de- 

 posits formed in 

 deep and shal- 

 low water, mostly 

 close to land. 



Sources. — The pelgaic deposits are made up in part of materials 

 of organic origin, and in part of materials of inorganic origin. The 

 inorganic materials may be of mechanical or chemical origin. Mechan- 

 ical pelagic deposits originate in various ways. They may come (1) from 

 the land by the ordinary processes of gradation, (2) from volcanic 

 vents, or (3) from extra-terrestrial sources. Chemical deposits may 

 be formed (1) in situ by the chemical interaction of substances in the 

 sea- water on materials of organic and inorganic origin, and (2) by 

 direct precipitation from the sea-water. 



Mechanical inorganic deposits. — ^The terrigenous materials which 

 reach the deep sea are, as a rule, only the finest products of land decay, 

 and are carried out by movements of water or by the winds. They are 

 not commonly recognized in the dredgings more than 200 miles from 

 the shore, but opposite the mouths of great rivers they extend much 

 farther, — 1000 miles in the case of the Amazon. They are especially 

 abundant on the slopes of the continental shelves. Here occur the 

 blue, green, and red muds, with which are associated volcanic and coral 

 muds. The color of these various muds is dependent in part on the 

 changes which they have undergone since their deposition. The green 

 muds usually contain enough glauconite to give them their color, and 

 are most commonly fotind off bold coasts where sedimentation is not 

 rapid. The blue muds indicate lack of oxidation, or perhaps deoxida- 

 tion. Red muds are not common, though they have been found in some 



