The _third_ great division of impressions in the sandstone rocks is
called PHYSICAL, meaning those made by inanimate and unorganized
substances; such are rain-drops, ripple-marks, and coprolites.
1. Marks of rain-drops, described on page 20, appear to be quite
common. We have two or three specimens in relief, and as many in
depression. They occur as follows: 1st, on the upper surface of the
slab first described; 2d, on that of the Platypterna; 3d, on that of
the AEthyopus Lyellianus; 4th, on that of the Brontozoum Gracillimum;
5th, on that of the AEthyopus Minor; 6th, on that of the Anomoepus
Scambus; 7th, on the recent clay; also in one small hand-specimen, and
in a second containing two fishes. They show that, in those ancient
periods when the Brontozoum Giganteum and the Otozoum resided in these
parts, showers were frequent, and probably abundant for the supply of
the wants and the gratification of the appetites of these animals,
then common, but which now appear to us so extraordinary.
2. Ripple-marks are seen in a number of these pieces; for example, on
the slab first described, on the Brontozoum Sillimanium slab, on the
Brontozoum Gracillimum slab, on one of the Triaenopus, and on the upper
surface of the Greenfield slab. These marks are represented by
parallel curves, or straight lines, distant from each other from half
an inch to an inch, and presenting a slight degree of prominence.
There is another form of ripple-marks(?), differing from those above
described. These are of a circular and mammillary form: they are
strewed thickly, like little islets, approximating to each other. They
are seen distinctly on one of the slabs of the Brontozoum Sillimanium,
on that of the AEthyopus Lyellianus, and some others. Whether they are
to be considered as accumulations of sand and clay, formed by the
action of the sea, we are uncertain; but there seems to be no other
cause to which they can be assigned with so great probability.
3. _Coprolites_, the fossilized ejections of animals, are intermixed
with other animal vestiges in the sandstone of Connecticut River, and
afford additional proof of the former existence of animals about these
rocks.
* * * * *
The latest accounts of fossil footprints we have had occasion to
notice are those of the Crustacea, already mentioned, as found in
Canada, and of the Chelonian in Scotland. The Canadian impressions,
called by Professor Owen Protichnites, were discovered in the year
1847, and were laid before the London Geological Society in 1851. The
most remarkable circumstance about them was their existence, as
already stated, in a white sandstone, near the banks of the River St.
Lawrence, at Beauharnais. This sandstone, which has been described by
New York geologists under the name of Potsdam, is thought to belong to
the Silurian system, and to have a higher antiquity than even the "old
red."
The Scotch footsteps are situated in the old red sandstone, and are
those of a Chelonian. So that we have now two series of tracks, the
Crustacea in Canada and the Chelonian in Scotland, of higher antiquity
than any which had been previously discovered.
* * * * *
On a review of the labors of President Hitchcock, we are struck with
admiration at the immense details that, in the midst of arduous
official and literary duties, he has been able to go through with in
the period since the foot-tracks were discovered on Connecticut River.
Although his labors should be modified by succeeding observers,
Science must be ever grateful to him for laying the foundation, and
doing so much for the completion, of a work so great, novel, and
interesting.
This inquiry seems to us to promise a rich variety; and we hope that
President Hitchcock and other observers will continue to explore and
cultivate it with undiminished zeal.