abundant, the number of species extended, and important additions made
in the traces of sea plants and fishes. Remains of fishes have been
detected in rocks immediately over the Aymestry limestone, being
apparently the first examples of vertebrated animals which breathed upon
our planet. (p. 64). The cephaloda, represented in our era by the
nautilus and cuttle-fish, pertain to the Silurian formation, and are the
most highly organised of the mollusca, possessing in some families an
internal bony skeleton, together with a heart and a head with mandibles
not unlike those of the parrot.

In the Old Red Sandstone the same marine specimens are continued with
numerous additions. Several of the strata are crowded with remains of
fish, showing that the seas in which these beds were deposited had
swarmed with that class of inhabitants. The predominating kinds are of
an inferior model to the two orders which afterwards came into
existence, and still are the principal fishes of our seas; the former
are covered with integuments of a considerably different character from
the true scales covering the latter, and which orders, from their form
of organization, are named stenoid and cycloid.

Up to the present we find proofs of the general uniformity of organic
life over the surface of the earth at the time when each particular
system of rocks was formed. The types of being formed in the old red as
in preceding deposits, are identical in species with the remains that
occur in the corresponding class of rocks in Brittany, the Hartz,
Norway, Russia, and North America; attesting the similarity and almost
universality, if not contemporary character, of terrestrial changes. A
few other geological facts may be here mentioned for recollection, and
which throw light on the marine animal and vegetable forms of this and
preceding eras. First there was comparatively an absence of salt in the