Seite - 361 - in The Origin of Species

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-