SUDDEN APPEARANCE OF GROUPS 361 



same with those since used by Sir W. Logan, have proved 

 true. Nevertheless, the difficuhy of assigning any good 

 reason for the absence of vast piles of strata rich in fossils 

 beneath the Cambrian system is very great. It does not seem 

 probable that the most ancient beds have been quite worn 

 away by denudation, or that their fossils have been wholly 

 obliterated by metamorphic action, for if this had been the 

 case we should have found only small remnants of the forma- 

 tions next succeeding them in age, and these would always 

 have existed in a partially metamorphosed condition. But 

 the descriptions which we 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 

 invariably it has suffered extreme denudation and meta- 

 morphism. 



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 vi^as derived, occurred 

 in the neighbourhood of the now existing continents of 

 Europe and North America. The 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 on an open and unfathomable sea. 



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

 sive 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 knowm to afford even a remnant of any palaeozoic and 

 secondary formation. Hence we may perhaps infer that 

 during the palaeozoic and secondary periods, neither conti- 



