surface of the earth has been geologically explored, and no part
with sufficient care, as the important discoveries made every year in
Europe prove. No organism wholly soft can be preserved. Shells and
bones will decay and disappear when left on the bottom of the sea, where
sediment is not accumulating. I believe we are continually taking a
most erroneous view, when we tacitly admit to ourselves that sediment
is being deposited over nearly the whole bed of the sea, at a rate
sufficiently quick to embed and preserve fossil remains. Throughout an
enormously large proportion of the ocean, the bright blue tint of the
water bespeaks its purity. The many cases on record of a formation
conformably covered, after an enormous interval of time, by another
and later formation, without the underlying bed having suffered in the
interval any wear and tear, seem explicable only on the view of the
bottom of the sea not rarely lying for ages in an unaltered condition.
The remains which do become embedded, if in sand or gravel, will when
the beds are upraised generally be dissolved by the percolation of
rain-water. I suspect that but few of the very many animals which live
on the beach between high and low watermark are preserved. For instance,
the several species of the Chthamalinae (a sub-family of sessile
cirripedes) coat the rocks all over the world in infinite numbers: they
are all strictly littoral, with the exception of a single Mediterranean
species, which inhabits deep water and has been found fossil in Sicily,
whereas not one other species has hitherto been found in any tertiary
formation: yet it is now known that the genus Chthamalus existed
during the chalk period. The molluscan genus Chiton offers a partially
analogous case.

With respect to the terrestrial productions which lived during the
Secondary and Palaeozoic periods, it is superfluous to state that our
evidence from fossil remains is fragmentary in an extreme degree. For
instance, not a land shell is known belonging to either of these
vast periods, with one exception discovered by Sir C. Lyell in the
carboniferous strata of North America. In regard to mammiferous remains,
a single glance at the historical table published in the Supplement to
Lyell's Manual, will bring home the truth, how accidental and rare is
their preservation, far better than pages of detail. Nor is their rarity
surprising, when we remember how large a proportion of the bones of
tertiary mammals h