appearance of new forms in any
one area and formation; that widely ranging species are those which have
varied most frequently, and have oftenest given rise to new species;
that varieties have at first been local; and lastly, although each
species must have passed through numerous transitional stages, it is
probable that the periods, during which each underwent modification,
though many and long as measured by years, have been short in comparison
with the periods during which each remained in an unchanged condition.
These causes, taken conjointly, will to a large extent explain
why--though we do find many links--we do not find interminable
varieties, connecting together all extinct and existing forms by the
finest graduated steps. It should also be constantly borne in mind that
any linking variety between two forms, which might be found, would be
ranked, unless the whole chain could be perfectly restored, as a new
and distinct species; for it is not pretended that we have any sure
criterion by which species and varieties can be discriminated.

He who rejects this view of the imperfection of the geological record,
will rightly reject the whole theory. For he may ask in vain where are
the numberless transitional links which must formerly have connected the
closely allied or representative species, found in the successive stages
of the same great formation? He may disbelieve in the immense intervals
of time which must have elapsed between our consecutive formations;
he may overlook how important a part migration has played, when the
formations of any one great region, as those of Europe, are considered;
he may urge the apparent, but often falsely apparent, sudden coming in
of whole groups of species. He may ask where are the remains of those
infinitely numerous organisms which must have existed long before the
Cambrian system was deposited? We now know that at least one animal did
then exist; but I can answer this last question only by supposing that
where our oceans now extend they have extended for an enormous period,
and where our oscillating continents now stand they have stood since the
commencement of the Cambrian system; but that, long before that epoch,
the world presented a widely different aspect; and that the older
continents, formed of formations older than any known to us, exist now
only as remnants in a metamorphosed condition, or lie still buried under
the ocean.

Passing from these difficulties, the other