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 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 again 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 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 the palaeozoic and
secondary periods, neither continents nor continental islands existed
where our oceans now extend; for had they existed there, palaeozoic and
secondary formations would in all probability have been accumulated from
sediment derived from their wear and tear; and would have been at least
partially upheaved by the oscillations of level, which we may fairly
conclude must have intervened during these enormously long periods. If
then we may infer anything from these facts, we may infer that where
our oceans now extend, oceans have extended from the remotest period of
which we have any record; and on the other hand, that where continents
now exist, large tracts of land have existed, subjected no doubt to
great oscillations of level, since the earliest silurian period. The
coloured map appended to my volume on Coral Reefs, led me to conclude
that the great oceans are still mainly areas of subsidence, the great
archipelagoes still areas of oscillations of level, and the continents
areas of elevation. But have we any right to assume that things have
thus remained from eternity? Our continents seem to have been formed
by a preponderance, during many oscillations of level,