134 The Bed of the Ocean. 



Formation of Areas of Elevation and of Areas of 

 Depression. — Assuming the previous deductions to be correct, 

 we can now conceive the formation of areas of elevation and 

 areas of depression, in consequence of the unequal distribution 

 of solid matter by oceanic currents, even in the absence of pre- 

 existing dry land, and antecedent to all other phenomena of 

 elevation and depression due to volcanic or other agencies. If 

 we suppose the whole surface of our planet covered with 

 water, the more rapid accumulation of solid matter in areas 

 where there is little or no current, and its slow deposit in 

 areas where strong currents prevail, would after a time divide the 

 bed of the ocean into plateaux and depressions. It is remark- 

 able that, while the direction of the principal mountain ranges is 

 so frequently from north to south, the direction of the lines which 

 divide the great river systems of our continents is generally from 

 east to west, which would imply that the longitudinal axis or central 

 ridge of the original plateaux, previous to the rising up of the 

 mountain ranges, was from east to west (Plate 4a). The con- 

 version of submarine plateaux into dry land would be effected 

 by the gradual rising of the areas of elevation through con- 

 tinuous accumulation of solid matter, simultaneously with the 

 deepening of the areas of depression through the removal of 

 deposits by currents, whose velocity must increase as their area 

 becomes more restricted. It may also be the result of a diminu- 

 tion in the total quantity of water contained in the ocean, or of 

 a retreat of the ocean, for there seems to be no argument to 

 prove that this quantity must be constant, or that the level of 

 the ocean must always be exactly at the same distance from the 

 centre of terrestrial gravity. On the contrary, if we separate the 

 centre of gravity of the whole mass of oceanic waters from the 

 centre of gravity of the solid portion of our planet, the former 

 may be subject to certain fluctuations, as the latter must be 

 affected by changes in the arrangement of the solid earth-crust. 



