SUBMARINE DEPOSITS. 



263 



The various kinds of deep-sea deposits are named after the 

 fragments or organisms predominating in each, or so numerous 

 as to be characteristic. 



The deposits found in more or less close proximity to conti- 

 nental shores are chiefly made up of the debris brought down 

 by rivers or torn away from the adjoining coasts. These are 



Fig. 178. — Black Spherule with metallic 

 nucleus. ^-^ . (Chall.) 3, 1.50 fathoms, 

 Atlantic. External coating removed to 

 show the metallic nucleus. (Chall.) 



Fig. 170. — Spherule covered with a coating 

 of black shining magnetite. The most 

 common shape showing the depression 

 found at the surface. '■^^. 2,375 fath- 

 oms, Pacific. (Chall.) 



called generally terrigenous deposits, and consist of quartz sands, 

 marls, blue, red, and green muds, and greensands. Around the 

 shores of volcanic islands and coral islands, the deposits are vol- 

 canic muds and sands, and coral muds and sands. 



Masses of rock, or huge boulders, but Httle altered, are found 

 close inshore, near the spot from which they originated. Far- 

 ther out, these are replaced by coarse shingle and gravel, 

 merging gradually, in the progress seaward, into the finer mate- 

 rial on the bottom. 



The fragments of quartz, feldspars, mica, together with frag- 

 ments of gneiss, granite, mica schist, and other ancient and 

 stratified rocks, which are very abundant in the deposits along 

 continental coasts, become gradually smaller in size and fewer 

 in number as we proceed towards the deeper and more distant 

 parts of the oceanic basins, when they become no longer re- 

 cognizable in the deposits, but form an impalpable ooze ; the 

 case, however, is different with those regions of the ocean which 

 are affected by floating ice and icebergs,^ and certain other 



^ Along our coasts, icebergs loaded northern regions drift south as far as lati- 

 with boulders and detritus brought from tude 36°, and distribute foreign material 



