Ichnology, a newly created branch of science, takes its name from the
Greek word _ichnos_, a _track_ or _footstep_, and the tracks
themselves have been denominated Ichnites, or, when they refer to
birds only, Ornithichnites, from _ornis_, a _bird_. And this last term
has by custom been generally applied to ancient impressions, though
not correctly.
Geology has revealed to us not only the remains of animals and
vegetables, but the impressions made by them during their lives, and
even the impressions of unorganized bodies. The first notice of these
appearances was, as often happens, regarded with indifference or
scepticism; but their number and variety enlightened the public mind,
and opened a new source of information and improvement.
The first remarkable observation made on fossil footsteps was that of
the Rev. Dr. Duncan, of Scotland, in 1828. He noticed, in a _new red
sandstone_ quarry in Dumfriesshire, impressions of the feet of small
animals of the tortoise kind, having four feet, and five toes on each
foot. They were seen in various layers through a thickness of forty
feet or more.
Sandstone, in which these impressions are principally discovered, is a
rock composed chiefly of siliceous and micaceous particles cemented
together by calcareous or argillaceous paste, containing salt, and
colored with various shades of the oxide of iron, particularly the
red, gray, brown. It has been remarked by Prof. H. D. Rogers, that the
perfection of the surface containing fossil footmarks is often
attributable to a micaceous deposit. The layers of sandstone have been
formed by deposits from sea-water, dried in succession; such layers
are also seen in the roofing slate. These deposits on the shores of
the ocean, having in a soft condition received the impressions of the
feet of birds, other animals, vegetables, and also of rain-drops,
under favorable circumstances dried, hardened, and formed a rock of
greater or less solidity. Our colleague, Dr. Gould, has exhibited to
us a specimen of dried clay from the shores of the Bay of Fundy,
containing beautiful impressions, recently made, of the footsteps of
birds. The particles brought by the waves, and deposited in the manner
described, were derived from the destruction of other rocks previously
existing, particularly granite and flint, or silex, the shining atoms
of which compose no small part of the sandstone rock.
It is easy to conceive, that, while these deposits were taking place
in the soft condition, portions of vegetable matters might become
intermixed; and that these, with the impressions of the feet and other
parts of animals and unorganized substances, might be preserved by the
process of desiccation. The agency of internal heat may have also been
employed in some cases in baking and hardening these crusty layers.
The sandstone rock, though in some places actually in a state of
formation at the present time, lies in such a manner in the earth's
crust as to indicate an immense antiquity. The age of these beds
varies in different situations. The sandstone rocks which contain the
greater part of the impressions are called _new red sandstone_, to
distinguish them from the _old red_, which is of a greater age. The
deposits on Connecticut River may not be attributed to the action of
this river, but are of higher antiquity, probably, than the river
itself, and proceeded from the waves of an ancient sea, existing in a
state of the surface of the globe very different from that of the
present day.
In 1834, tracks were discovered near Hildberghausen in Saxony, to
which Prof. Kaup, of Darmstadt, gave the name of Chirotherium, from
the resemblance to the impressions of the human hand. On a subsequent
examination, Prof. Owen preferred the name of Labyrinthodon, from the
resemblance of the folds in the teeth to the convolutions of the
brain.
Various other instances of impressions were seen; and, in the year
1835, Dr. Deane and Mr. Marsh, residents of Greenfield, noticed
impressions resembling the feet of birds in sandstone rocks of that
neighborhood. These observations having come to the knowledge of
President Hitchcock, of Amherst College, that gentleman began a
thorough investigation of the subject, followed it up with unremitted
ardor, and has, since 1836 (the date of his first publication), laid
before the public a great amount of ichnological information, and
really created a new science. Dr. Deane, on his part, has not been
idle: besides making valuable discoveries, he has written a number of
excellent papers to record some portion of his numerous observations.
In 1837, at the request of my friend Dr. Boott, I carried to London,
for the Museum of the Royal College of Surgeons, various scientific
objects peculiar to this country; among which were a number of casts
of Ornithichnites.
These casts were kindly furnished me by President Hitchcock, and the
Government of the Royal College thereon voted to present to President
Hitchcock and Amherst College casts of the skeleton of the famous
Megatherium of South America. These casts were packed, and sent to be
embarked in a ship destined for Boston, but were unluckily delivered
to a wrong shipping house in London, and I lost sight of them for some
time. They were at length discovered. After remaining in this
situation for more than a year, they were sold at public auction; and,
notwithstanding many efforts on my part, I was unable to obtain and
transmit them to Amherst College.
The fossil impressions which have been distinguished in various places
in the new red sandstone are those of birds, frogs, turtles, lizards,
fishes, mollusca, crustacea, worms, and zoophytes. Besides these, the
impressions made by rain-drops, ripple-marks in the sand, coprolites
or indurated remains of faeces of animals, and even impressions of
vegetables, have been preserved and transmitted from a remote
antiquity. No authentic human impressions have yet been established;
and none of the mammalia, except the marsupials.(?) We must, however,
remember that, although the early paleontology contains no record of
birds, the ancient existence of these animals is now fully
ascertained. Remains of birds were discovered in the Paris gypsum by
Cuvier previous to 1830. Since that time, they have been found in the
Lower Eocene in England, and the Swiss Alps; and there is reason to
believe that osseous relics may be met with in the same deposits which
contain the foot-marks. Most of the bird-tracks which have been
observed, belong to the wading birds, or Grallae.
The number of toes in existing birds varies from two to five. In the
fossil bird-tracks, the most frequent number is three, called
tridactylous; but there are instances also of four or tetradactylous,
and two or didactylous. The number of articulations corresponds in
ornithichnites with living birds: when there are four toes, the inner
or hind toe has two articulations, the second toe three, the third toe
four, the outer toe five. The impressions of the articulations are
sometimes very distinct, and even that of the skin covering them.
President Hitchcock has distinguished more than thirty species of
birds, four of lizards, three of tortoises, and six of batrachians.
The great difference in the characters of many fossil animals from
those of existing genera and species, in the opinion of Prof. Agassiz,
makes it probable that in various instances the traces of supposed
birds may be in fact traces of other animals, as, for example, those
of the lizard or frog. And he supports this opinion, among other
reasons, by the disappearance of the heel in a great number of
Ornithichnites.
D'Orbigny, to whom we are indebted for the most ample and systematic
work on Paleontology ("Cours Elementaire de Paleontologie et de
Geologie," 5 vols. 1849-52), does not accept the arrangement of
President Hitchcock. He objects to the term Ornithichnites, and
proposes what he considers a more comprehensive arrangement into
organic, physiological, and physical impressions. _Organic
impressions_ are those which have been produced by the remains of
organized substances, such as vegetable impressions from calamites,
&c. _Physiological impressions_ are those produced by the feet and
other parts of animals. _Physical impressions_ are those from
rain-drops and ripple-marks; and to these may be added coprolites in
substance. This plan of D'Orbigny seems to exclude the curious and
interesting distinctions of groups, genera, and species; in this way
diminishing the importance of the science of Ichnology.
Fossil impressions have been found on this continent in the
carboniferous strata of Nova Scotia, and of the Alleghenies; in the
sandstone of New Jersey, and in that of the Connecticut Valley in a
great number of places, from the town of Gill in Massachusetts to
Middletown in Connecticut, a distance of about eighty miles.
A slab from Turner's Falls, obtained for me by Dr. Deane in 1845,
measuring two feet by two and a half, and two inches in thickness,
contains at least ten different sets of impressions, varying from five
inches in length to two and a half, with a proportionate length of
stride from thirteen inches to six. All these are tridactylous, and
represent at least four different species. In most of them the
distinction of articulation is quite clear. The articulations of each
toe can readily be counted, and they are found to agree with the
general statement made above as to number. The impressions are
singularly varied as to depth; some of them, perfectly distinct, are
superficial, like those made by the fingers laid lightly on a mass of
dough, while others are of sufficient depth nearly to bury the toes;
some of the tracks cross each other, and, being of different sizes,
belong to animals of different ages or different species. There is one
curious instance of the tracks of a large and heavy bird, in which,
from the softness of the mud, the bird slipped in a lateral direction,
and then gained a firm footing; the mark of the first step, though
deep, is ill-defined and uncertain; the space intervening between the
tracks is superficially furrowed; in the settled step, which is the
deepest, the toes are very strongly indicated. On the same surface are
impressions of nails, which may have belonged to birds or chelonians.
The inferior surface of the same slab exhibits appearances more
superficial, less numerous, but generally regular. There are three
sets of tracks entirely distinct from each other; two of them
containing three tracks, and one containing two,--the latter being
much the largest in size. In addition, there is one set of tracks,
which are probably those of a tortoise. These marks present two other
points quite observable and interesting. One is that they are
displayed in relief, while those on the upper surface are in
depression. The relief in this lower surface would be the cast of a
cavity in the layer below; so the depressions in the upper surface
would be moulds of casts above. The second point is the
non-correspondence of the upper and lower surfaces; i.e. the
depressions in the upper surface have not a general correspondence
with the elevations on its inferior surface. The tracks above were
made by different individuals and different species from those below.
This leads to another interesting consideration, that in the thickness
of this slab there must be a number of different layers, and in each
of them there may be a different series of tracks.
To these last remarks there is one exception: the deep impression in
which the bird slipped in a lateral direction corresponds with an
elevation on the lower surface, in which the impression of these toes
is very distinctly displayed, and even the articulations. Moreover,
one of the tracks on the inferior surface interferes with the outer
track in the superior, and tends in an opposite direction, so that
this last-described footstep must have been made before the other. It
is also observable, that, while all the other tracks are superficial,
this last penetrates the whole thickness of the slab; thus showing
that the different deposits continued some time in a soft state.
On the surfaces of this slab, particularly on the upper, there are
various marks besides those of the feet, some of which seem to have
been made by straws, or portions of grass, or sticks; and there is a
curved line some inches in length, which seems to have arisen from
shrinkage.
In the collection of Mr. Marsh,[B] there were two slabs of great size,
each measuring ten by six feet, having a great number of impressions
of feet, and about the same thickness as the slab under examination.
One of these presented depressions; and the other, corresponding
reliefs. These very interesting relations were necessarily parted in
the sale of Mr. Marsh's collection; one of them being obtained for the
Boston Society of Natural History, and the other for the collection of
Amherst College.
[Footnote B: Mr. Marsh was a mechanic of the town of Greenfield,
and procured his subsistence by his daily labor. Being employed by
Dr. Deane in obtaining the sandstone slabs of Ornithichnites, he
acquired a taste for the pursuit, entered into it with
extraordinary ardor, and accumulated by his own labors a great
collection of fine specimens. He unfortunately fell into a
consumption, and died in 1852. The collection was sold at public
auction for a sum between two and three thousand dollars. The
specimens were purchased by the Boston Society of Natural History,
by Amherst College, and by varioud colleges and scientific
associations in this country.]
The _Physical Impressions_, according to Professor D'Orbigny, are
of three kinds, viz.: 1st, Rain-drops; 2d, Ripple-marks; and 3d,
Coprolites. I have a slab which exhibits two leptodactylous
tracks very distinct, about an inch and a half long, surrounded
by impressions of rain-drops and ripple-marks. Another specimen
exhibits the impressions of rain in a more distinct and remarkable
manner. The imprints are of various sizes, from those which might
be made by a common pea to others four times its diameter; some
are deep, others superficial and almost imperceptible. They are
generally circular, but some are ovoid. Some have the edge equally
raised around, as if struck by a perpendicular drop; and others
have the edge on one part faintly developed, while another part is
very sharp and well defined, as if the drop had struck obliquely.
It has been suggested, that these fossil rain-drops may have been
made by particles of hail; but I think the variety of size and
depth of depression would have been more considerable if thus
made.
Although we have necessarily treated the subject of fossil
footmarks in a very brief way, sufficient has been said to show
that this new branch of Paleontology may lead to interesting
results. The fact that they are, in some manner, peculiar to this
region, seems to call upon our Society to obtain a sufficient
number of specimens to exhibit to scientific men a fair
representation of the condition of Ichnology in this quarter of
our country; and we have therefore great reason to congratulate
ourselves, that, through the vigilance and spirit of our members,
the Society has the expectation of obtaining a rich collection
of ichnological specimens.