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, of the force of
elevation; but may not the areas of preponderant movement have changed
in the lapse of ages? At a period immeasurably antecedent to the
silurian 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 formations older than the silurian
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 bare 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
silurian epoch in a completely metamorphosed condition.
The several difficulties here discussed, namely our not finding in the
successive formations infinitely numerous transitional links between
the many species which now exist or have existed; the sudden manner in
which whole groups of species appear in our European formations; the
almost entire absence, as at present known, of fossiliferous formations
beneath the Silurian strata, are all undoubtedly of the gravest nature.
We see this in the plainest manner by the fact that all the most
eminent pal ontologists, namely Cuvier, Owen, Agassiz, Barrande,
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