294 THE ORIGIN OF SPECIES 



intervals existed as dry land, or as a submarine surface near land, 

 on which sediment was not deposited, or as the bed of an open 

 and unfathomable sea. 



Looking to the existing oceans, which are thrice as extensive 

 as the land, we see them studded with many islands; but hardly 

 one truly oceanic island (with the exception of New Zealand, if 

 this can be called a truly oceanic island) is as yet known to afford 

 even a remnant of any palaeozoic or secondary formation. Hence, 

 we may perhaps infer, that during the palaeozoic and secondary 

 periods, neither continents nor continental islands existed where 

 our oceans now extend; for had they existed, palaeozoic and sec- 

 ondary formations would in all probability have been accumulated 

 from sediment derived from their wear and tear; and these would 

 have been at least partially upheaved by the oscillations of level, 

 which must have intervened during these enormously long periods. 

 If, then, we may infer anything from these facts, we may infer 

 that, where our oceans now extend, oceans have extended from 

 the remotest period of which we have any record; and on the 

 other hand; that where continents now exist, large tracts of land 

 have existed, subjected, no doubt, to great oscillations of level, 

 since the Cambrian period. The colored map appended to my 

 volume on Coral Reefs led me to conclude that the great oceans 

 are still mainly areas of subsidence, the great archipelagoes still 

 areas of oscillations of level, and the continents areas of elevation. 

 But we have no reason to assume that things have thus remained 

 from the beginning of the world. Our continents seem to have 

 been formed by a preponderance, during many oscillations of level, 

 of the force of elevation. But may not the areas of preponderant 

 movement have changed in the lapse of ages? At a period long 

 antecedent to the Cambrian epoch, continents may have existed 

 where oceans are now spread out, and clear and open oceans may 

 have existed where our continents now stand. Nor should we be 

 justified in assuming that if, for instance, the bed of the Pacific 

 Ocean were now converted into a continent, we should there find 

 sedimentary formations, in recognizable condition, older than the 

 Cambrian strata, supposing such to have been formerly deposited; 

 for it might well happen that strata which had subsided some 

 miles nearer to the centre of the earth, and which had been 

 pressed on by an enormous weight of superincumbent water, 

 might have undergone far more metamorphic action than strata 

 which have always remained nearer to the surface. The immense 

 areas in some parts of the world, for instance in South America, 

 of naked metamorphic rocks, which must have been heated under 



