276 ON THE ORIGIN OF SPECIES 



nodules and bituminous matter in some of the lowest 

 azoic rocks, probably indicates the former existence of 

 life at these periods. But the difficulty of understand- 

 ing the absence of vast piles of fossiliferous strata, 

 which on my theory no doubt were somewhere accumu- 

 lated before the Silurian epoch, is very great. If 

 these most ancient beds had been wholly worn away 

 by denudation, or obliterated by metamorphic action, 

 we ought to find only small remnants of the forma- 

 tions next succeeding them in age, and these ought to 

 be very generally in a metamorphosed condition. But 

 the descriptions which we now possess of the Silurian 

 deposits over immense territories in Russia and in 

 North America, do not support the view, that the 

 older a formation is, the more it has always suffered 

 he extremity of 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 neighbourhood of the existing continents of Europe 

 and North America. But we do not know what was 

 the state of things in the intervals between the suc- 

 cessive 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 not one oceanic island is as yet known to 

 afford even a remnant of any palaeozoic or secondary 

 formation. Hence we may perhaps infer, that during 



