Chap. IX. IN LOWEST FOSSILIFEROUS STRATA. 293 



Lookinp^ lo the existing oceans, whicli are thrice as exten- 

 sive as the hind, we see them studded with many ishmds ; but 

 not one truly oceanic ishind (with the exception of New Zea- 

 hind, if this can be called a truly oceanic island) is as ^-^et known 

 to afford even a renmant of any jialeozoic or secondary forma- 

 tion. Hence we may perhaps infer that, duriufr the paleozoic 

 and secondary periods, neither continents nor continental islands 

 existed where our oceans now extend ; for had they existed, 

 ])aleozoicand secondary formations would in all j)roi)ability have 

 been accumulated from sediment derived from their wear and 

 tear ; and these would have been at least partiall}' upheaved 

 by the oscillations of level, which must have intervened during 

 these enormousl3'-long' periods. If, then, we may infer any 

 thing 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 

 cofitinents now exist, large tracts of hind have existc.'d, subjected 

 no doubt to great oscillations of level, since the earliest Silurian 

 j)criod. The colored map appended to my volume on Coral 

 lleefs led me to conclude that the great oceans are still mainly 

 areas of subsidence, the great archipelagoes still areas of oscil- 

 lations of level, and the continents areas of elevation. IJut 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 jireponderance, during many oscillations of level, 

 of the force of elevation ; but may not the areas of preponder- 

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

 long antecedent to the Silurian epoch, continents may have ex- 

 isted where oceans are now spread out ; and clear and open 

 oceans may have existed where our continents now stand. Nor 

 should we be justilied in assuming that if, for instance, the bed 

 of the Pacific Ocean were now converted into a continent, we 

 shouUl there find sedimentary formations in a recognizable con- 

 dition older than the Silurian strata, suj^posing 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 undergcme far more met- 

 amorphic action than strata Avhich 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 great pressure, have 

 always seemed to me to require some special explanation; and 



