that
during the palaeozoic and secondary periods, neither continents nor
continental islands existed where our oceans now extend; for had they
existed, 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 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 Cambrian 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 we have no reason to assume that things have
thus remained from the beginning of the world. Our continents seem to
have been formed by a preponderance, during many oscillations of
level, of the force of elevation. But may not the areas of preponderant
movement have changed in the lapse of ages? At a period long antecedent
to the Cambrian epoch, continents may have existed where oceans are
now spread out, and clear and open oceans may have existed where our
continents now stand. Nor should we be justified in assuming that if,
for instance, the bed of the Pacific Ocean were now converted into a
continent we should there find sedimentary formations, in recognisable
condition, older than the Cambrian strata, supposing such to have been
formerly deposited; for it might well happen that strata which had
subsided some miles nearer to the centre of the earth, and which had
been pressed on by an enormous weight of superincumbent water, might
have undergone far more metamorphic action than strata which have always
remained nearer to the surface. The immense areas in some parts of the
world, for instance in South America, of naked metamorphic rocks, which
must have been heated under great pressure, have always seemed to me to
require some special explanation; and we may perhaps believe that we see
in these large areas the many formations long anterior to the Cambrian
epoch in a completely metamorphosed and denuded condition.

The several di