224 THE OCEAN 



numbers of crystals assuming a spherical 

 form of small size (see Plate XII.). 



Rate of Deposition. — From observations 

 made by telegraph cable engineers in the North 

 Atlantic it is believed that globigerina ooze 

 accumulates, in lat. 50° N., long. 30° W., at 

 the rate of an inch in about ten years in 2300 

 fathoms, and in lat. 3° N., long. 30° W., at a 

 somewhat more rapid rate in 1900 fathoms, 

 while recent investigations indicate that in 

 certain positions deposition may be hindered 

 even in depths exceeding 1000 fathoms by 

 tidal currents. Theoretically it may be 

 assumed that terrigenous deposits accumulate 

 much more rapidly than pelagic deposits, 

 and this is confirmed by observations, a maxi- 

 mum rate of deposition being found near land, 

 especially off the mouths of large rivers, and 

 a minimum rate in those red clay areas farthest 

 removed from continental land in very deep 

 water. 



Radio-active Matter, — From a study of some 

 representative samples of deep-sea deposits 

 supplied by the writer, J. Joly has 

 found that the radium-content is much 

 higher in deep-sea deposits than in terrestrial 

 rocks, and that red clays and radiolarian oozes 

 from very deep water contain much more 

 radium than the calcareous pteropod and 

 globigerina oozes from shallower depths. It 



