IN LO WEST F088ILIFER0 US STB A TA. Ml 



the oscillations of level, which must have iutervened 

 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 oscilla- 

 tions of level, and the continents areas of elevation. But 

 we have no reason to assume that things have thus re- 

 mained 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 center 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 sur- 

 face. 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 explana- 

 tion; and we may perhaps believe that we see in these 

 large areas the many formations long anterior to the Cam- 

 brian epoch in a completely metamorphosed and denuded 

 condition. 



The several difficulties here discussed, namely, that, 

 though we find in our geological formations many links 

 between the species which now exist and which formerly 



