Of the ninth group, containing the marks of Annelidae, Crustacea, and
Zoophytes, we have various specimens.
The impressions of insects do not seem as yet to have been
distinguished on the ancient rocks. There is reason to believe,
however, that many of the marks we discover in the rocky beds might
have been made by the feet and bodies of large insects; and small
species of the same tribes have been found imbedded in, and actually
constituting, immense masses of calcareous and siliceous rocks.
The tracks of worms are numerous. No doubt these worms drew together a
concourse of birds to the shores on which they rolled. On various
slabs we find long cylindrical furrows, about the eighth of an inch in
diameter, and of different lengths; one of them, in the slab from Dr.
Deane, being eight or nine inches long. To these impressions the name
of HERPYSTEZOUM, from _herpystes_, _crawling_, has been given. They
vary, however, and some of them are very likely to be the tracks of
the common earth-worm, or of some species of worm which existed when
these rocks were formed. These impressions vary in length and in
diameter; some of them are moderately regular, and others irregularly
curved.
Very interesting tracks have been found in the ancient Potsdam white
sandstone of Beauharnais, on the St. Lawrence, by Mr. Logan, an
excellent geologist of Canada, and determined by Professor Owen to
belong to Crustacea, crabs. The number of impressions made by each
foot is sometimes seven, sometimes eight, and even more. This track,
showing the traces of Crustacea, goes to form another link in the
chain of fossil footsteps.
The Medusae, commonly called jelly-fish, dissolving as they do under
the influence of the sun and air, would hardly be expected to leave
their traces impressed on ancient rocks. Professor D'Orbigny, however,
has watched the dissolution of these animals on the sea-shore, and
found that, after wasting, they may leave their impressions on the
sand; which, not being disturbed by a high tide for nearly a month,
retains the impression of the zoophyte, and serves as a mould to
receive materials which take a cast and transmit it to subsequent
ages. We find one of these impressions on the slab of the Anomoepus
Scambus; and President Hitchcock, having examined it, is of opinion
that it retains the traces of a Medusa. The impression is about five
inches in diameter, of a darker color and smoother texture than the
rest of the rock. Its edges fade away gradually in the surface of the
subjacent sandstone. A similar impression is found on the superior
surface of the slab containing the Argozoum.
* * * * *