II PERMANENCE OF THE GREAT OCEANIC BASINS 33 



scale, elevation and subsidence must nearly balance each 

 other, and, thus, in order that any area of continental 

 magnitude should rise from the ocean floor till it formed 

 fairly elevated dry land, some corresponding area must 

 sink to a like extent. But if such subsiding area formed 

 a part or the whole of a continent, the land would entirely 

 disappear beneath the waters of the ocean (except a few 

 mountain peaks) long before the corresponding part of 

 the ocean floor had approached the surface. In order, 

 therefore, to make any such interchange possible, without 

 the total disappearance of the greater portion of the sub- 

 siding continent before the new one had appeared to take 

 its place, we must make some arbitrary assumptions. We 

 must sup2)ose either that when one portion of the ocean 

 floor rose, some other part of that floor sank to greater 

 depths till the new continent approached the surface, or, 

 that the sinking of a whole continent was balanced by the 

 rising of a comparatively small area of the ocean floor. 

 Of course, either of these assumed changes are conceivable 

 and, perhaps, possible ; but it seems to me that they are 

 exceedingly improbable, and that to assume that they have 

 occurred again and again, as part of the regular course 

 of the earth's history, leads us into enormous difficulties. 

 Consider, for a moment, what would be implied by the 

 building up of a continent the size of Africa from the 

 mean depth of the ocean. By comparing the area of 

 Africa with that of the whole of the land, and the depth 

 of the ocean with the mean height of the land, we shall 

 And that if all the land of the globe above sea-level could 

 be transferred to mid-ocean, it would not be sufficient to 

 form the new continent, but would still leave it nearly 

 2,000 feet beneath the surfxce. 



It thus appears that, if the elevation of the ocean floor, 

 and the corresponding sinking of whole continents, con- 

 stitute a portion of the regular change and development 

 of the earth's surface, there would be not only a chance 

 but a very great probability of entire continents disappear- 

 ing beneath the waters before even the smallest new 

 continent had risen to take their place. Even the total 

 disappearance of all the large land masses might easily 



VOL. 1. i) 



