Many of our readers must have heard of the interest excited a few
years ago by the discovery, that certain marks on the surface of slabs
of sandstone, raised from a quarry in Dumfriesshire, were the
memorials of extinct races of animals. The amiable and intelligent Dr
Duncan, minister of Ruthwell, who had conferred on society the
blessing of savings-banks for the industrious poor, was the first to
describe to the world these singular chronicles of ancient life. The
subject was afterwards brought forward in a more popular style by Dr
Buckland, in his lively book, the Bridgewater Treatise on Geology.
Since then, examples of similar markings have been found in several
other parts of Europe, and a still greater number in America.
Dumfriesshire is still the principal locality of these curious objects
in our island; and they are found not only in the original spot--the
quarry of Corncockle Muir, but in another quarry at Craigs, near the
town of Dumfries. Ample collections of them have been made by Sir
William Jardine, the famed naturalist, who happens to be proprietor of
Corncockle Quarry, and by Mr Robert Harkness of Dumfries, a young
geologist, who seems destined to do not a little for the illustration
of this and kindred subjects. Meanwhile, Sir William Jardine has
published an elegant book, containing a series of drawings, in which
the slabs of Corncockle are truthfully represented.[4]
The Annandale footmarks are impressed on slabs of the New Red
Sandstone--a formation not long subsequent to the coal, and remarkable
for its comparative deficiency of fossils, as if there had been
something in its constitution unfavourable to the preservation of
animal remains. It is curious to find that, while this is the case, it
has been favourable to the preservation of what appears at first sight
a much more accidental and shadowy memorial of life--the mere
impression which an animal makes on a soft substance with its foot.
Yet such fully appears to be the fact. The sandstone slabs of
Corncockle, lying in their original place with a dip of about 33
degrees to the westward, and separating with great cleanness and
smoothness, present impressions of such liveliness, that there is no
possibility of doubt as to their being animal foot-tracks, and those
of the tortoise family. A thin layer of unctuous clay between the beds
has proved favourable to their separation; and it is upon this
intervening substance that the marks are best preserved. Slab after
slab is raised from the quarry--sometimes a foot thick, sometimes only
a few inches--and upon almost every one of them are impressions found.
What is very remarkable, the tracks or series of footprints pass,
almost without exception, in a direction from west to east, or upwards
against the dip of the strata. It is surmised that the strata were
part of a beach, inclining, however, at a much lower angle, from which
the tide receded in a westerly direction. The animals, walking down
from the land at recess of tide, passed over sand too soft to retain
the impressions they left upon it; but when they subsequently returned
to land, the beach had undergone a certain degree of hardening
sufficient to receive and retain impressions, 'though these,' says Sir
William, 'gradually grow fainter and less distinct as they reach the
top of the beds, which would be the margin of drier sands nearer the
land.' He adds: 'In several instances, the tracks on one slab which we
consider to have been impressed at the same time, are numerous, and
left by different animals travelling together. They have walked
generally in a straight line, but sometimes turn and wind in several
directions. This is the case in a large extent of surface, where we
have tracks of above thirty feet in length uncovered, and where one
animal had crossed the path of a neighbour of a different species. The
tracks of two animals are also met with, as if they had run side by
aide.'
With regard to the nature of the evidence in question, Dr Buckland has
very justly remarked, that we are accustomed to it in our ordinary
life. 'The thief is identified by the impression which his shoe has
made near the scene of his depredations. The American savage not only
identifies the elk and bison by the impression of their hoofs, but
ascertains also the time that has elapsed since the animal had passed.
From the camel's track upon the sand, the Arab can determine whether
it was heavily or lightly laden, or whether it was lame.' When,
therefore, we see upon surfaces which we know to have been laid down
in a soft state, in a remote era of the world's history, clear
impressions like those made by tortoises of our own time, it seems a
legitimate inference, that these impressions were made by animals of
the tortoise kind, and, consequently, such animals were among those
which then existed, albeit no other relic of them may have been found.
From minute peculiarities, it is further inferred, that they were
tortoises of different species from any now existing. Viewing such
important results, we cannot but enter into the feeling with which Dr
Buckland penned the following remarks:--'The historian or the
antiquary,' he says, 'may have traversed the fields of ancient or of
modern battles; and may have pursued the line of march of triumphant
conquerors, whose armies trampled down the most mighty kingdoms of the
world. The winds and storms have utterly obliterated the ephemeral
impressions of their course. Not a track remains of a single foot, or
a single hoof, of the countless millions of men and beasts whose
progress spread desolation over the earth. But the reptiles that
crawled upon the half-finished surface of our infant planet, have left
memorials of their passage, enduring and indelible. No history has
recorded their creation or destruction; their very bones are found no
more among the fossil relics of a former world. Centuries and
thousands of years may have rolled away between the time in which
those footsteps were impressed by tortoises upon the sands of their
native Scotland, and the hour when they were again laid bare and
exposed to our curious and admiring eyes. Yet we behold them, stamped
upon the rock, distinct as the track of the passing animal upon the
recent snow; as if to shew that thousands of years are but as nothing
amidst eternity--and, as it were, in mockery of the fleeting,
perishable course of the mightiest potentates among mankind.'
The formation of the slabs, and the preservation of the footprints,
are processes which the geologist can easily explain. A beach on which
animals have left the marks of their feet, becomes sufficiently
hardened to retain the impressions; another layer of sand or mud is
laid down by perhaps the next tide, covering up the first, and
protecting it from all subsequent injury. Thousands of years after,
the quarryman breaks up the layers, and finds on the one surface the
impression of the animal, while the lower face of the superincumbent
layer presents a cast of that impression, thus giving us in fact a
double memorial of one event. At Wolfville, on the Bay of Fundy, Sir
Charles Lyell some years ago observed a number of marks on the surface
of a red marly mud which was gradually hardening on the sea-shore.
They were the footprints of the sand-piper, a bird of which he saw
flights daily running along the water's edge, and often leaving thirty
or more similar impressions in a straight line, parallel to the
borders of the estuary. He picked up some slabs of this dried mud, and
splitting one of them up, found a surface within which bore two lines
of the same kind of footprints. Here is an example before our living
eyes, of the processes concerned in producing and preserving the
fossil footprints of the New Red Sandstone.
Some years after the Annandale footprints had attracted attention,
some slab surfaces of the same formation in Saxony and England were
found bearing an impression of a more arresting character. It
resembled the impression that would be made by the palm and extended
fingers and thumb of the human hand, but a hand much thicker and
flabbier than is commonly seen. The appropriate name of
_Cheirotherium_ was proposed for the unknown extinct animal which had
produced these marks. The dimensions in the several examples were
various; but 'in all cases the prints of what appear to have been the
hind-feet are considerably larger than those of the fore-feet; so much
so, indeed, that in one well-preserved slab containing several
impressions, the former measures eight inches by five, and the latter
not more than four inches by three. In this specimen, the print of the
fore-foot is not more than an inch and a half in advance of that of
the hinder one, although the distance between the two successive
positions of the same foot, or the length of a pace of the animal, is
fourteen inches. It therefore appears, that the animal must have had
its posterior extremities both much larger and much longer than the
anterior; but this peculiarity it possessed in common with many
existing species, such as the frog, the kangaroo, &c.; and beyond this
and certain appearances in the sandstone, as if a tail had been
dragged behind the animal, in some sets of footsteps, but not in
others, there is nothing to suggest to the comparative anatomist any
idea of even the class of Vertebrata to which the animal should be
referred.'[5] Soon after, some teeth and fragments of bones were
discovered, by which Professor Owen was able to indicate an animal of
the frog-family (Batrachia), but with certain affinities to the
saurian order (crocodiles, &c.), and which must have been about the
size of a large pig. It has been pretty generally concluded, that this
colossal frog was the animal which impressed the hand-like
foot-prints.
At a later period, footprints of birds were discovered upon the
surfaces of a thin-bedded sandstone belonging to the New Red formation
on the banks of the Connecticut River, in North America. The birds,
according to Sir Charles Lyell, must have been of various sizes; some
as small as the sand-piper, and others as large as the ostrich, the
width of the stride being in proportion to the size of the foot. There
is one set, in which the foot is nineteen inches long, and the stride
between four and five feet, indicating a bird nearly twice the size of
the African ostrich. So great a magnitude was at first a cause of
incredulity; but the subsequent discovery of the bones of the Moa or
Dinornis of New Zealand, proved that, at a much later time, there had
been feathered bipeds of even larger bulk, and the credibility of the
_Ornithichnites Giganteus_ has accordingly been established. Sir
Charles Lyell, when he visited the scene of the footprints on the
Connecticut River, saw a slab marked with a row of the footsteps of
the huge bird pointed to under this term, being nine in number,
turning alternately right and left, and separated from each other by a
space of about five feet. 'At one spot, there was a space several
yards square, where the entire surface of the shale was irregular and
jagged, owing to the number of the footsteps, not one of which could
be distinctly traced, as when a flock of sheep have passed over a
muddy road; but on withdrawing from this area, the confusion gradually
ceased, and the tracks became more and more distinct.'[6] Professor
Hitchcock had, up to that time, observed footprints of thirty species
of birds on these surfaces. The formation, it may be remarked, is one
considerably earlier than any in which fossil bones or other
indications of birds have been detected in Europe.
In the coal-field of Westmoreland county, Pennsylvania, there were
discovered in 1844, slabs marked with footprints bearing a
considerable resemblance to those of the Cheirotherium, and believed
to have been impressed by an animal of the same family, though with
some important points of distinction. The hind-feet are not so much
larger than the fore; and the two on each side, instead of coming
nearly into one row, as in the European Cheirotherium, stand widely
apart. The impressions look such as would be made by a rudely-shaped
human hand, with short fingers held much apart; there is some
appearance as if the fingers had had nails; and a protuberance like
the rudiment of a sixth finger appears at the side. This was the
first indication of reptile life so early as the time of the
coal-formation; but as the fossil remains of a reptile have now been
found in Old Red Sandstone, at Elgin, in Scotland, the original
importance of the discovery in this respect may be regarded as
lessened.
Last year, some slabs from Potsdam, in Canada, were brought to
England, and deposited in the museum of the Geological Society.
Belonging as these slabs do to a formation coeval with those in which
the earliest fossils were hitherto found, it was startling to find
them marked with numerous foot-tracks of what appeared to have been
reptiles. It seemed to shew, that the inhabitants of the world in that
early age were not quite so low in the scale of being as had
previously been assumed from the facts known; and that all attempts to
describe, from positive knowledge, anything like a progression of
being on the face of our globe, were at least premature. Professor
Owen had, at first, scarcely any hesitation in pronouncing the
footprints to be those of tortoises; but he afterwards changed his
views, and expressed his belief that the impressions had been produced
by small crustacean animals. Thus the views previously entertained
regarding the invertebrate character of the _fauna_ of the Silurian
epoch, have ultimately remained unaffected, so far as these Potsdam
slabs are concerned.
Slabs of sandstone and shale often retain what is called the
ripple-mark--that is, the corrugation of surface produced by the
gentle agitation of shallow water over sand or mud. We can see these
appearances beneath our feet, as we walk over the pavement of almost
any of our cities. Such slabs are also occasionally marked by
irregular protuberances, being the casts of hollows or cracks produced
in ancient tide-beaches by shrinkage. In many instances, the
footprints of animals are marked by such lines passing through them,
shewing how the beach had dried and cracked in the sun after the
animals had walked over it. In the quarries at Stourton, in Cheshire,
some years ago, a gentleman named Cunningham observed slab surfaces
mottled in a curious manner with little circular and oval hollows, and
these were finally determined to be the impressions produced by
rain--the rain of the ancient time, long prior to the existence of
human beings, when the strata were formed! Since then, many similar
markings have been observed on slabs raised from other quarries, both
in Europe and America; and fossil rain-drops are now among the settled
facts of geology. Very fine examples have been obtained from quarries
of the New Red Sandstone at Newark and Pompton, in New Jersey. Sir
Charles Lyell has examined these with care, and compared them with the
effects of modern rain on soft surfaces of similar materials. He says,
they present 'every gradation from transient rain, where a moderate
number of drops are well preserved, to a pelting shower, which, by its
continuance, has almost obliterated the circular form of the cavities.
In the more perfectly preserved examples, smaller drops are often seen
to have fallen into cavities previously made by larger ones, and to
have modified their shape. In some cases of partial interference, the
last drop has obliterated part of the annular margin of a former one;
but in others it has not done so, for the two circles are seen to
intersect each other. Most of the impressions are elliptical, having
their more prominent rims at the deeper end [a consequence of the rain
falling in a slanting direction]. We often see on the under side of
some of these slabs, which are about half an inch thick, casts of the
rain-drops of a previous shower, which had evidently fallen when the
direction of the wind was not the same. Mr Redfield, by carefully
examining the obliquity of the imprints in the Pompton quarries,
ascertained that most of them implied the blowing of a strong westerly
wind in the triassic period at that place.' A certain class of the
impressions at Pompton are thought to be attributable to hail, 'being
deeper and much more angular and jagged than the rain-prints, and
having the wall at the deeper end more perpendicular, and occasionally
overhanging.'[7]