on the beach between high and low watermark are preserved. For
instance, the several species of the Chthamalin (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 Pal ozoic 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
have been discovered either in caves or in lacustrine deposits; and
that not a cave or true lacustrine bed is known belonging to the age of
our secondary or pal ozoic formations.
But the imperfection in the geological record mainly results from
another and more important cause than any of the foregoing; namely,
from the several formations being separated from each other by wide
intervals of time. When we see the formations tabulated in written
works, or when we follow them in nature, it is difficult to avoid
believing that they are closely consecutive. But we know, for instance,
from Sir R. Murchison s great work on Russia, what wide gaps there are
in that country between the superimposed formations; so it is in North
America, and in many other parts of the world. The most skilful
geologist, if his attention had been exclusively confined to these
large territories, would never have suspected that during the periods
which were blank and barren in his own country, great piles of
sediment, charged with new and peculiar forms of life, had elsewhere
been accumulated. And if in each separate territory, hardly any idea
can be formed of the length of time which has elapsed between the
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