orns,
Herefordshire, and Alderney breeds of cattle{419}. I have attempted to
show that rising islands, in process of formation, must be the best
nurseries of new specific forms, and these points are the least
favourable for the embedment of fossils{420}: I appeal, as evidence, to
the state of the _numerous_ scattered islands in the several great
oceans: how rarely do any sedimentary deposits occur on them; and when
present they are mere narrow fringes of no great antiquity, which the
sea is generally wearing away and destroying. The cause of this lies in
isolated islands being generally volcanic and rising points; and the
effects of subterranean elevation is to bring up the surrounding
newly-deposited strata within the destroying action of the coast-waves:
the strata, deposited at greater distances, and therefore in the depths
of the ocean, will be almost barren of organic remains. These remarks
may be generalised:--periods of subsidence will always be most
favourable to an accumulation of great thicknesses of strata, and
consequently to their long preservation; for without one formation be
protected by successive strata, it will seldom be preserved to a distant
age, owing to the enormous amount of denudation, which seems to be a
general contingent of time{421}. I may refer, as evidence of this
remark, to the vast amount of subsidence evident in the great pile of
the European formations, from the Silurian epoch to the end of the
Secondary, and perhaps to even a later period. Periods of elevation on
the other hand cannot be favourable to the accumulation of strata and
their preservation to distant ages, from the circumstance just alluded
to, viz. of elevation tending to bring to the surface the
circum-littoral strata (always abounding most in fossils) and destroying
them. The bottom of tracts of deep water (little favourable, however, to
life) must be excepted from this unfavourable influence of elevation. In
the quite open ocean, probably no sediment{422} is accumulating, or at a
rate so slow as not to preserve fossil remains, which will always be
subject to disintegration. Caverns, no doubt, will be equally likely to
preserve terrestrial fossils in periods of elevation and of subsidence;
but whether it be owing to the enormous amount of denudation, which all
land seems to have undergone, no cavern with fossil bones has been found
belonging to the Secondary period{423}.

{419} _Origin_, Ed. i. p. 299, vi. p. 437.