and, as Dr. Dawson has remarked, certainly preyed on other
minute organic beings, which must have lived in great numbers. Thus the
words, which I wrote in 1859, about the existence of living beings long
before the Cambrian period, and which are almost the same with those
since used by Sir W. Logan, have proved true. Nevertheless, the
difficulty 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 formations 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 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 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 unfathomable 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 secondary formation. Hence, we may perhaps infer,