340 GROUPS OF ALLIED SPECIES 



does not seem probable that the most ancient beds have 

 been quite worn away by denudation, or that their fossils 

 have been wholly obliterated oy metamorphic action, for 

 if this had been the case we should have found only small 

 remnants of the formations next succeeding them in age, 

 aud these would always have existed in a partially meta- 

 morpliosed condition. But the descriptions which we 

 possess of the silurian deposits over immense territories in 

 Russia and in Xorth America, do not support the view 

 that the older a formation is the more invariably it has 

 sutfored extreme denudation and metamorphism. 



The case at present must remain inexplicable, and may 

 be truly urged as a valid argument against the views here 

 entertained. To show that it may hereafter receive some 

 explanation, I will give the following hypothesis. From 

 the nature of the organic remains 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 neighborhood of the now existing conti- 

 nents 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 

 unfathomable sea. 



Looking to the existing oceans, which are thrice as ex- 

 tensive 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 secondary formation. Hence, we may perhaps infer, 

 that during the pala3ozoic and secondary periods, neither 

 continents nor continental islands existed where our oceans 

 now extend; for had they existed, palaeozoic and second- 

 ary formations would in all probability have been accumu- 

 lated from sediment derived from their wear and tear; 

 and these would have been at least partially upheaved by 



