288 GROUPS OF SPECIES IN LOWEST STRATA [Chap. X. 



which do not appear to have inhabited profound depths, in the 

 several formations of Europe and of the United States ; and from 

 the amount of sediment, miles in thickness, of which the formations 

 are composed, we may infer that from first to last large islands 

 or tracts of land, whence the sediment was derived, occurred in the 

 neighbourhood of the now existing continents of Europe and 

 North America. This same view has since been maintained by 

 Agassiz and others. But we do not know what was the state 

 of things in the intervals between the several successive formations ; 

 whether Europe and the United States during these intervals 

 existed as dry land, or as a submarine surface near land, on which 

 sediment was not deposited, or as the bed of an open and unfathom- 

 able sea. 



Looking to the existing oceans, which are thrice as extensive as 

 the land, we see them studded with many islands ; but hardly one 

 truly oceanic island (with the exception of New Zealand, if this 

 •can be called a truly oceanic island) is as yet known to afford even 

 a remnant of any palaeozoic or secondaiy formation. Hence we may 

 perhaps infer, that during the palaeozoic and secondary periods, 

 neither continents nor continental islands existed where our oceans 

 now extend ; for had they existed, palaeozoic and secondary forrnc- 

 tions would in all probability have been accumulated from sediment 

 derived from their wear and tear ; and these would have been at 

 least partially upheaved by the oscillations of level, which 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 Cambrian period. The 

 coloured map appended to my volume on Coral Eeefs, 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 beginning of the world. 

 Our continents seem to have been formed by a ijreponderance, during 

 many oscillations of level, of the fcrce 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, con- 

 tinents 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 



