ir 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.

* * * * *

GROUP TENTH.

The tenth group contains the HARPAGOPUS, a name derived from
_harpage_, _seizure_, _rapine_. It is represented by President
Hitchcock as having the form of a drag. The figure given by him
resembles in a degree the foot of the African ostrich; being a long
thick toe, with a shorter one, not unlike a thumb, on the side. An
impression approximating this, but of small size, may be seen on the
slab of the Anomoepus Scambus.

* * * * *

The formation of bird-tracks is well represented by a clay specimen,
about an inch thick, and ten inches long. This is a piece of dried
clay, obtained by President Hitchcock from the banks of the
Connecticut, and produced by washings from clay on the shore above,
covered with foot-impressions of a small tridactylous bird, and dried
in the sun. This piece shows, in a way not to be questioned, the
manner in which the ancient vestiges were produced. Sir Charles Lyell
noticed a similar fact on the banks of the Bay of Fundy.

ORGANIC IMPRESSIONS.

The _second_ great division of fossil impressions is called ORGANIC,
meaning impressions made by organized bodies; the bones of animals,
fishes, and vegetables.

Near one extremity of the slab of the Ornithopus Gallinaceus is an
elevation, about a foot long, and between one and two inches wide,
projecting from the surface nearly half an inch. It has the appearance
of a round bar of iron imbedded in the rock, which is clayey
sandstone. This apparent bar of iron was probably a bone, buried in
the stone, now silicified and impregnated with iron; the animal matter
having entirely disappeared. In the slab of the Brontozoum Sillimanium
is a