Remarks on some fossil impressions in the sandstone rocks of Connecticut River

GROUP FIRST—STRUTHIONES

The ostrich-tracks present a numerous natural and most remarkable group; remarkable from the great size of some species,—all of them tridactylous and pachydactylous. The ostrich of the Old World has only two toes, but this family exists in South America at the present time under the name of Rhea Americana; and tracks of an animal, probably of the same family, are found in the numerous impressions near Connecticut River,—all of them having three toes in front, and the rudiment of a fourth behind.

This group contains a number of genera. The First Genus, denominated Brontozoum, presents the tracks of a most extraordinary bird. These tracks appear less questionable since the discovery in Madagascar of the eggs of the Epyornis.

The tracks of the largest species, the Brontozoum Giganteum, are four times the magnitude of those made by the existing ostrich of Africa. They are very numerous, and congregated together. The foot of the Brontozoum Giganteum, including the inferior extremity of the tarso-metatarsal bone, which makes a part of the foot, measures in our specimen twenty inches; in the Mastodon Giganteus, the foot measures twenty-seven inches; the width also is less, being ten inches across the metacarpals, while that of the Mastodon is twenty-two: but the one is a bird, the other a quadruped. The toes are three in number, and present the same divisions with existing birds; the inner toe having three, the middle four, the outer five phalanges. Some of the articulations of the toes of this noble specimen are remarkable for the manner in which they illustrate the mode of formation of the tracks. These phalanges have become separated from the solid rock in which they were encased, so as to be removable at pleasure; and they thus show that the whole foot is not a simple impression in the rock which contains it, but a depression filled by foreign materials, i.e. by sand, clay, and other relics of pre-existing rocks. These materials had been gradually deposited in the mould formed by the bird's foot, and are therefore independent of this rock, in the same way as the plaster-of-Paris cast of a tooth, or any other body, is independent of the mould to which it owes its form. The impressions are in gray sandstone.

On the reversed surface of the slab is seen a small piece of broken quartz, about half an inch square. This piece forms a beautiful illustration of a part of the process by which the sandstone rocks are formed.

The second species of the same genus is the Brontozoum Sillimanium. Of this we have three specimens; the tracks have the same general character with the preceding, but are smaller.

The third species of this genus is styled the Brontozoum Loxonyx, from λοξὸς, a bow, and ὄνυξ, a nail,—a curved nail. It is smaller than the Sillimanium, and has the nail set to one side.

The fourth species, still smaller, is the Brontozoum Gracillimum. On this slab the impressions are in relief; viz.: 1st, of Brontozoum Gracillimum; 2d, of Brontozoum Parallelum; 3d, of the track of a tortoise, fourteen inches long, and two wide. Other extensive eminences and depressions, with rain-drops, may be observed on the same surface.

The fifth species is called Brontozoum Parallelum, from the tracks being on a line with each other. Of this there are two specimens, one of them, however, being a single track. On the surface of the other slab there are at least five distinct tracks, one of them being a small new and undescribed species,—thus making the whole number of species of Brontozoum which we possess to be at least six.

The Second Genus of Struthiones is called Æthyopus, from αἴθυια, a gull, and ποὺς, a foot,—gull-footed. This genus is smaller than the Brontozoum Giganteum; and we have two species, viz. the Æthyopus Lyellianus, which is the larger, and two specimens of Æthyopus Minor. All of these are distinguished from the preceding genus by the winged foot, and in the Lyellianus by the shallowness of the impression. The Æthyopus Minor is not always distinguished by the superficiality of its impression. This is sometimes deep. Therefore this character may not be considered a distinctive one, or the Æthyopus Minor might be referred to another genus. Of the two specimens of this latter species, the first is in depression, tridactylous. The depressions are deep with rain-drops, marks of quadrupeds and zoophytes over the whole surface. The ornithichnic impressions are two in number; one superficial, the other very deep. The reversed surface of this slab contains one tridactylous impression in relief. The second specimen has three depressions; two of which are superficial, and the third is quite deep, displaying, by a depressed surface, the webbed character of the foot.

GROUP SECOND

We shall take, to characterize this group, the Argozoum, from ἀργὴς, swift, winged.

Of this genus there are two species, the larger of which is the Argozoum Disparidigitatum. It is leptodactylous, and remarkable for the length of the middle toe. We have another species, which is smaller than the last named, and in which the toes are nearly of equal length; hence called Argozoum Paridigitatum.

The other genus of this group is the Platypterna, and our specimen is named Deaniana. This genus is remarkable for the width of the heel; hence the name, from πλατὺς, broad, and πτέρνη, a heel. It has three toes like the other genera of this group.

GROUP THIRD

This and the succeeding group are tetradactylous; having one toe behind, three forwards.

The third group is leptodactylous; foot usually small, but sometimes of medium size. Of it we have two specimens, viz.: Ornithopus Gallinaceus, and Ornithopus Gracilis. The former is so called from the resemblance to the domestic fowl: for convenience sake, in this and other instances, we use the whole for a part. It is about three inches in length, and the Ornithopus Gracilis about two.

This latter specimen is particularly interesting. It consists of two parts, which open like the covers of a book. These covers present four impressions: first, the superficial, which is distinct, slender, and beautiful—the heel is broad; second, corresponding with this depression and on the inside, is a figure in relief as distinct as the depression; third, on the inside of the second cover is a depression corresponding with the relief last mentioned; fourth, on the outer side is a second relief corresponding with the second depression, but less distinct than either of the other three, still, however, exhibiting three toes pointing anteriorly, but the hind toe is wanting. The whole of this double slab forms a series of cameos and intaglios, measuring four inches by three, and in thickness an inch and a quarter.

GROUP FOURTH

Of the fourth group we have five specimens. The Triænopus, so called from its resemblance to a trident, has besides three leptodactylous toes pointing forwards, a fourth extending backwards in a remarkable way, like the handle of a trident; the impression, however, being expanded so as to show an extensive displacement of the mud. All the specimens of Triænopus are in a beautiful red shale, very thin and fragile, but presenting well-defined impressions, generally about three inches long.

There are two species to this genus. Of the Triænopus Emmonsianus we notice three impressions in relief. In another specimen there is the appearance of a part of the toes of the Anomœpus Scambus, and on the upper side are seen two excavations corresponding with the three impressions. In the last slab, the track of the Triænopus Baileyanus appears to have been made by two feet placed successively in the same spot, which led President Hitchcock to suspect it might have been made by a quadruped. One of the specimens has the Triænopus tracks intermixed in a peculiar way with other impressions.

The specimen representing the genus Harpedactylus is larger than the preceding; and, though leptodactylous, the toes are much broader and also more curved, whence the name Harpedactylus, sickle-finger, from ἅρπη and δάκτυλος.

GROUP FIFTH

The fifth group differs much from the four previous ones. In this and the following groups we pass from the vestiges of birds to those of other animals, some of which are bipeds, some quadrupeds. Many impressions are without any distinct character, belonging probably to the lower animals, to vegetables, and unorganized bodies.

The fifth group comprehends the tracks of an extraordinary animal, the Otozoum.3 The name which has been given to it is taken from that of an ancient giant, Otus, who with his brother Ephialtes, according to heathen mythology, made war with the gods. These fabled giants were, at nine years of age, nine cubits in width and nine fathoms in height.

The foot is divided into four toes; the two outer of which seem to be connected by a common basis. The inner toe has three phalanges; the second toe, also three; the third and fourth toes, four each. The first is the shortest, the second longer, the third longest, the fourth shorter than the third. It will appear, then, that this track differs from that of birds in the number of toes pointing forwards; these being four, while in birds the forward toes are only three. There is a difference also in the number and arrangement of the articulations.

The track in our possession is twenty inches long by thirteen and a half inches broad. The rock in which it is imbedded is a dark-colored sandstone. President Hitchcock has a slab showing a regular series of tracks of this animal; the distance between the steps being about three feet, and the tracks equidistant and alternate, which would not be the case if the animal had been quadrupedal. In a quadruped, the horse for example, the hind feet are set down near the fore feet, and sometimes even strike them. Hence it must be inferred that the track in question was that of a biped, or of a quadruped which did not use its fore feet in progression, like a kangaroo. We naturally ask, What kind of biped could this have been? Evidently not a man, the size of the foot being too large to admit such a supposition; nor could it have been a bird, the number of toes and their direction not admitting this hypothesis.

Tetradactylous birds, or those which have four toes, have only three of them directed forwards, and the fourth backwards, generally. There are, however, exceptions; some birds have four toes directed forwards: this is the fact with the Hirundo Cypselus and the Pelicanus Aquilus of Linnæus, or Man-of-war Bird. But the articulations are different in the two animals, birds having regularly two, three, four, and five phalanges, and the spur, where it exists, supported by a single osseous phalanx; whereas the Otozoum has three phalanges in the inner and second toe, four in the third and fourth toes. In this last arrangement, the Otozoum is decidedly different from all known birds. It is not likely to have been a tortoise or a lizard. The kangaroo has four feet, and uses only two in progression, moving forward by leaps; also, like the Otozoum, it has four toes; but the size of the toes does not accord with that of the Otozoum, nor is the structure of the foot the same, so far as we know. It has been suggested by Professor Agassiz, that this animal might have been a two-footed frog. Nature had, in those days, animal forms different from those we are acquainted with; and this might have been the fact with the Otozoum.

GROUP SIXTH

We have in this group a specimen of the track of a four-footed animal, which may have been a frog, though different from ours. The feet are unequal in size, and present a different number of toes. In existing frogs there are four toes in the fore feet, and five in the hind; but, in the specimen before us, the front toes are five in number, and the back toes three. It is called, therefore, Anomœpus, unequal-footed. These impressions are in the red shale of Hadley, and very distinct. In some of them the lower leg is indicated, forming an impression six or seven inches long. The feet being smaller than the legs, the impression made by the latter is more expanded, superficial, and broader, yet still very definite. The opinion of President Hitchcock and Dr. Deane is, that the different impressions of five and three toes are those of the anterior and posterior extremities of one animal, which, from the size of the limbs, might be a frog three feet high.

On the same schist with these footmarks, are other curious impressions. The back of the slab is almost covered with the imprints of rain-drops. In the midst of these is a tridactylous impression, probably of a quadruped, crossed at its root by a single depression, nearly an inch broad, and two and a half long: this seems to form part of another broad superficial impression of about seven by four inches, which is probably also quadrupedal. Other parts present the impressions of nails and worm-tracks. At the opposite end is a deep, smooth, regular excavation, which might have been made by a Medusa.

GROUP SEVENTH

The seventh group contains the impressions of the feet of Saurians or lizards. We have a specimen of quadrupedal marks, with five toes to each foot, about an inch long, which may have been made by these animals. The impressions are small, but very distinct. There are lizards of the present day with five toes, about the size of these impressions; and these may, therefore, be set down as belonging to this order of reptiles. Like a number of the last-named specimens, they are in red shale.

GROUP EIGHTH

The eighth group is assigned by President Hitchcock to the Chelonian or turtle tribe. The slab bearing impressions of Brontozoum Gracillimum has a mark about fourteen inches long and two wide, which may be attributed to the plastron or breast-plate of the tortoise. On the slab from Turner's Falls there is a longitudinal furrow, which might have been made by the tail of a turtle; and in various of our slabs are impressions which we think belong to this tribe. We shall have occasion to notice hereafter remarkable tracks of these animals in the old red of Morayshire, in Scotland.

The most distinct of the traces of chelonians are on the large slab lately obtained for me by President Hitchcock from Greenfield. (Vide Plate.) This interesting slab contains the traces of quadrupeds, various birds, and two trails of chelonians: the largest of these is nearly five feet long, and four inches in diameter. The trail is composed of a number of parallel elevations, comparatively superficial.

GROUP NINTH

Of the ninth group, containing the marks of Annelidæ, 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 ἑρπυστὴς, 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 Medusæ, 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 Anomœpus 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 ἁρπαγὴ, 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 Anomœpus 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 projection about seven or eight inches long, and half an inch wide; probably the bone of an animal, perhaps a clavicle of the Brontozoum Giganteum.

The vestiges of fishes are very numerous in the sandstone rocks of Connecticut River. We have not less than two dozen specimens from this locality; a number equal to all the other specimens in our collection. These impressions of fishes are generally from three to six inches long, and three or four inches wide. They are of the grand division denominated by Professor Agassiz "heterocercal," having their tails unequally bilobed, from the partial prolongation of the dorsal spine; and they are considered to be of lower antiquity than the fishes which are entirely heterocercal. The most remarkable of the fish-specimens in our collection is a Cephalaspis (?): this fish is found in the specimen containing tracks of the Brontozoum Gracillimum, and traces of a turtle or tortoise. This fossil was discovered in the upper layer of the old red sandstone of Scotland, and had been mistaken by some for a trilobite: to us it appeared to be a Limulus, but further observation leads us to believe it to be a Cephalaspis. It exhibits a convex disc, four inches across, by two inches from above downwards, and a tail at right angles with the disc, the uncovered part of which is three inches long. The animal has been described by Professor Agassiz as being composed of a strong buckler, with a pointed horn at either termination of the crescent, and an angular tail.

To the vegetable impressions discovered among the sandstone rocks a peculiar name has not yet been assigned. When, however, we consider the strong probability that many impressions of stalks, leaves, fruits, and other parts of vegetables, may be hereafter discovered in these rocks, it will be found convenient to have a distinctive denomination. Vast numbers of vegetable impressions of a distinct and beautiful appearance, and in great variety, have been found in the coal-formation, which is nearly allied to the sandstone: such are the Sigillaria, Stigmaria, Equisetaceæ, Lycopodiaceæ, Coniferæ, Cycadeæ, &c. It is sufficient to say that the number of these has been already swelled to many hundreds: we must also believe, that some of the impressions in sandstone rocks which have been assigned to other substances ought to be attributed to vegetables. We may, therefore, venture to call the vegetable impressions "phytological."

A number of our slabs bear impressions of vegetables; either twigs of trees, or spires of plants. In a fragment broken from one of the toes of the Brontozoum Giganteum, we see a cylindrical depression, three inches long, and half an inch in diameter, marked by transverse lines, about the sixth of an inch apart, and presenting an unquestionable appearance of a fragment of a twig of an ancient vegetable, which had been trodden under the foot of the mighty Brontozoum. On the reversed surface of the same slab are found impressions, which were produced by a number of fragments of sticks, five or six inches long, lying at right angles, or nearly so. One of these sticks has been broken, and its pieces are slightly displaced from each other. Various other specimens contain the marks of sticks, or twigs of trees. The striæ, so distinctly discernable in a number of these portions, having been compared with twigs of the existing coniferæ (?), were found to resemble them. Some of these sticks show the appearance of incipient carbonization; yet the rock is sandstone, presenting, as already mentioned, distinct appearances of quartz, and other substances of which the arenaceous rocks are composed.

PHYSICAL IMPRESSIONS

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 Æthyopus Lyellianus; 4th, on that of the Brontozoum Gracillimum; 5th, on that of the Æthyopus Minor; 6th, on that of the Anomœpus 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 Triænopus, 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 Æthyopus 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.