Chap. X.] IN LOWEST FOSSILIPEEOUS STRATA. 87 



land have existed, subjected no doubt to great oscilla- 

 tions of level, since the Cambrian period. The col- 

 oured 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 eleva- 

 tion. 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 preponder- 

 ance, during many oscillations of level, of the force of 

 elevation; but may not the areas of preponderant move- 

 ment 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. N'or should we be justified in assuming 

 bhat if, for instance, the bed of the Pacific Ocean were 

 now converted into a continent we should there find 

 £edimentary formations in a recognisable condition older 

 than the Cambrian strata, supposing such to have been 

 formerly deposited; for it might well happen that strata 

 which had subsided some milesnearerto 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 al- 

 ways 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 we may per- 

 haps believe that we see in these large areas, the many 

 formations long anterior to the Cambrian epoch in a 

 completely metamorphosed and denuded condition. 



