rates
consisting, according to his arrangement, of three great
divisions,--mollusca, articulata, and radiata; and the vertebrates, of
four great classes,--the mammals, the birds, the reptiles, and the
fishes. From the lowest zone at which organic remains occur, up till
the higher beds of the Lower Silurian System, all the animal remains yet
found belong to the invertebrate divisions. The numerous tables of stone
which compose the leaves of this first and earliest of the geologic
volumes correspond in their contents with that concluding volume of
Cuvier's great work in which he deals with the mollusca, articulata, and
radiata; with, however, this difference, that the three great divisions,
instead of occurring in a continnous series, are ranged, like the
terrestrial herbs and trees, in parallel columns. The chain of animal
being on its first appearance is, if I may so express myself, a
threefold chain;--a fact nicely correspondent with the further fact,
that we cannot in the present creation range _serially_, as either
higher or lower in the scale, at least two of these divisions,--the
mollusca and articulata. In one of the higher beds of the Upper Silurian
System,--a bed which borders on the base of the Old Red Sandstone,--the
vertebrates make their earliest appearance in their fourth or ichthyic
class; and we find ourselves in that volume of the geologic record which
corresponds to Cuvier's volume on the fishes. In the many-folded pages
of the Old Red Sandstone, till we reach the highest and last, there
occur the remains of no other vertebrates than those of this fourth
class; but in its uppermost deposits there appear traces of the third or
reptilian class; and in passing upwards still, through the
Carboniferous, Permian, and Triassic Systems, we find reptiles
continuing the master existences of the time. The geologic volume in
which these great formations are included corresponds to the Cuvierian
one devoted to the Reptilia. Early in the Oolitic System, birds,
Cuvier's second class of the vertebrata, make their first appearance,
though their remains, like those of birds in the present time, are rare
and infrequent; and, for at least the earlier periods of their
existence, we know that they were,--that they haunted for food the
waters of the period, and waded in their shallows,--only from marks
similar to those by which Crusoe became first aware of the visits paid
to his island by his savage neighbors,--their footprint