IMPERFECTION OF GEOLOGICAL RECORD 93 



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 vol- 

 ume 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 begin- 

 ning 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 a recog- 

 nizable condition older than the Cambrian strata, suppos- 

 ing 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 ac- 

 tion 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 meta- 



