Chap. IX. GEOLOGICAL KECORD. 309 



tear ; and would have been at least partially upheaved 

 by the oscillations of level, which we may fairly con- 

 clude 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 earliest silurian period. The coloured 

 map appended to my volume on Coral Keefs, 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 have we any right to assume that things have thus 

 remained from eternity ? Our continents seem to have 

 been formed by a preponderance, during many oscilla- 

 tions 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 immeasurably antecedent to 

 the silurian 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 formations older 

 than the silurian 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 enor- 

 mous 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 bare metamorphic rocks, which 



