,8,, THE PERMANENCE OF OCEANIC BASTNS. 423 



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 

 geological epochs, they would have produced 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 mountainous 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, 

 notwithstanding these various forms of upheaval, involving vertical 

 displacements which are sometimes several miles in extent, the 

 surface of the land often 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 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 irregulari- 

 ties in the ocean floor far greater than those which occur upon the 

 land surface. 



Still more difficult to explain would be the absence of pre- 

 cipitous escarpments due to faults, which, though frequently 

 showing an upthrow or downthrow of the strata to the amount of 

 many hundreds and sometimes thousands of feet, rarely exhibit any 

 difference of level on the land surface, owing to the fact that subaerial 

 denudation has kept pace with slow and intermittent elevation. But 

 in the ocean depths no such denudation is going on ; and we can there- 

 fore only account for its very uniform surface on the supposition that 

 it is not subject to the varied and complex subterranean movements 

 which have certainly acted within the continental areas throughout 

 known geological time. 3 



Equal Range of the Geological Record in all the Continents. — There is 

 one other general consideration which indicates the permanence and 

 continuity of the Continental Areas, and which renders it very diffi- 



^ The Rev. O. Fisher has arrived at this conclusion from his own researches. 

 He says : " The compression -which has caused the thickening accompanied by 

 corrugation, such as characterises most elevated tracts, is properly a continental 

 phenomenon, and has no analogue beneath the oceans." L.c, p. 253. 



