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.
Pages:
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375