II PERMANENCE OF THE GREAT OCEANIC BASINS 37 



both Palaeozoic and Mesozoic, or Mcsozoic and Tertiary. 

 This would necessarily be the case, because we cannot 

 believe that so vast a change as the subsidence of an entire 

 continent till its site became a deep ocean, and its subse- 

 quent elevation till it again became dry land, could 

 possibly be effected in any less extended periods, if at all. 

 Whenever such gaps, or smaller ones, now occur locally, 

 they are generally held to imply the existence of terrestrial 

 conditions, as in the case of China, which, according to 

 Richthoven, has been continental since the Carboniferous 

 epoch. In many cases there is distinct evidence of such 

 conditions in lacustrine or freshwater deposits, dirt-beds, 

 &c. But if a gap of such vast extent, both in space and 

 time, as that here referred to were caused by the inter- 

 change of a continent and a deep ocean, the fact that it 

 was so produced would be clearly evidenced by an almost 

 uniform deposit either of organic or clayey ooze, similar 

 to those now everywhere forming over the oceanic area. 

 Even if we make the fullest allowance for denudation 

 during elevation, sufficient indications of so widespread a 

 formation should be detected. Such a deposit would, in 

 fact, have every chance of being largely preserved, because, 

 long before it rose to the level where it would be subject 

 to denudation by waves or currents, it would, almost every- 

 where, be overlain by a series of shore deposits, and where- 

 ever these latter were preserved on the land surface the 

 oceanic formation would necessarily be found under them. 

 That no such enormous deficiency in the geological series 

 characterises any of the continents, and that no widespread 

 deposit of organic or clayey ooze at some definite horizon 

 has been anywhere detected, though such a deposit must 

 have been formed and largely preserved if the whole or 

 any considerable part of a continent had risen from ocean 

 depths at any period of its history, constitute of themselves 

 very strong arguments against any such interchange of 

 oceanic and continental areas having occurred. 



Summary of the Argument. 



I have now shown that there are three distinct groups 

 of phenomena which are either altogether inconsistent 



