132 T. C. CHAM BERLIN 



By way of approach and qualification let it be noted that while 

 these deposits mantle the bed of the deep sea very generally and 

 must be presumed to have been essentially free from the agitating 

 effects of sea waves and similar superficial agencies, the special 

 locations in which such deposits accumulated most largely were yet 

 somewhat influenced by even such currents as affect the abysmal 

 waters. The larger part of the finely divided material of the 

 abysmal deposits, whether it came from surface organisms or from 

 dust or wash, floated long before it finally found lodgment at the 

 bottom of the deep sea, and hence slight differences of motion 

 determined whether given particles came to rest at a particular 

 point or floated on to a quieter spot. The circulation of the deep 

 sea is relatively gentle, but still there is the circulation actuated by 

 the differences of temperature between the equatorial and polar 

 regions, and the differences of density between the belts of heavy 

 precipitation and the belts of active evaporation, not to speak of 

 motion communicated by friction from the surface currents actu- 

 ated by the winds, tides, and other familiar agencies. If the great 

 sea basins have been essentially permanent throughout geologic 

 history, a point we shall urge a little later, the long persistence of the 

 currents of the deep circulation have made cumulative differences 

 in the growth of the abysmal deposits, and some fraction, greater 

 or less, of the undulations and the smoothed surfaces that charac- 

 terize the ocean bottoms signify differences of deposition, even 

 though the deposition at any one time has been small compared 

 with the volume of sedimentation that took place in an equal time 

 near the sea border. It is observed that on many submarine 

 slopes and ridges no fine mud is deposited because of the strong 

 currents that sweep the bottom clear. ^ In the upper half of the 

 ocean depth the movement of the currents has been measured 

 ins trumen tally ; in the lower half, positive data are scant, but it 

 is clear that the diversion of the great abysmal currents of water, as 

 they encounter continental or other obstacles to their progress, is 

 likely to give rise to concentrated or quickened currents at the criti- 

 cal points of arrest and deflection. 



But, although such inequalities of deposition must be recog- 

 ■ Murray and Hjort, The Depths of the Ocean (191 2), p. 272. 



