II PERMANENCE OF THE GREAT OCEANIC BASINS 35 



of submerged mountain ranges — precipices, deep valleys 

 and ravines, arranged in diverging groups as they always 

 occur in nature. But in no single case, that I am aware 

 of, have any such features been discovered. 



But a still greater difficulty remains to be considered. 

 If oceanic and continental areas are interchangeable, it 

 can only be because the very same causes (whatever they 

 may be) that produce elevations and subsidences in the 

 one produce them also in the other, and at first sight it 

 appears probable that this would be the case. But if 

 these causes have been at work upon the ocean floor 

 throughout all geological epochs, they would have pro- 

 duced irregularities of surface not less but far greater than 

 on subaerial land. This must be so, because subaerial 

 denudation continually neutralises much of the effect of 

 upheaval in the continental areas, while in the ocean 

 depths no such cause or anything analogous to it is 

 in operation. 



The forces which have been at work in every moun- 

 tainous region have sometimes tilted up great masses of 

 rock at high angles, upheaved them into huge anticlinal 

 curves, or crushed them by lateral pressure into repeated 

 folds, which in some cases appear to have fallen over so 

 as to reverse the succession of the strata. But, notwith- 

 standing these various forms of upheaval, involving vertical 

 displacements which are sometimes several miles in extent, 

 the surface of the land usually shows no corresponding 

 irregularities, owing to the fact that subaerial denudation 

 has either kept pace with upheaval or has even exceeded 

 it, so that the position of an anticlinal ridge may be, and 

 often is, represented by a valley. Now, if we suppose that 

 similar upheaving forces have been at work on that portion 

 of the earth's surface forming the bed of the ocean where 

 there are no such counteracting agencies, we should expect 

 to find irregularities in the ocean floor far greater than 

 those which occur upon the land surface. 



Still more difficult to explain would be the absence of 

 precipitous escarpments due to faults, which, though fre- 

 quently showing an upthrow or downthrow of the strata 

 to the amount of many hundreds and sometimes many 



D 2 



