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
palaeontologists, namely Cuvier, Owen, Agassiz, Barrande, Falconer,
E. Forbes, etc., and all our greatest geologists, as Lyell, Murchison,
Sedgwick, etc., have unanimously, often vehemently, maintained the
immutability of species. But I have reason to believe that one great
authority, Sir Charles Lyell, from further reflexion entertains grave
doubts on this subject. I feel how rash it is to differ from these great
authorities, to whom, with others, we owe all our knowledge. Those who
think the natural geological record in any degree perfect, and who do
not attach much weight to the facts and arguments of other kinds given
in this volume, will undoubtedly at once reject my theory. For my part,
following out Lyell's metaphor, I look at the natural ge