It is now about twenty-six years since Dr Duncan of Ruthwell first brought fossil footprints under the notice of geologists. These, when first discovered, were so unique, that Dr Buckland, to whom the subject was first intimated, was disposed to consider these footmarks as either fossil shells partially decomposed, or clay concretions. After inspecting casts forwarded him by Dr Duncan, he arrived at the conclusion that these impressions were veritable footprints left by animals which existed at the epoch when the red sandstone of Dumfriesshire was being deposited; this being the formation in which these footsteps are found. After the discovery of impressions in the sandstone of Corncockle Muir, Dumfriesshire, the attention of geologists became directed to this subject; and in a short while other districts were found to afford fossil tracks. Amongst these the new red sandstone of Hildburghausen, in Saxony, furnished specimens of Batrachian forms; similar tracks were also obtained at Stourton quarry, on the south side of the Mersey, opposite Liverpool, and at Lynne also, in Cheshire. Afterwards the same county afforded this form of step, in conjunction with the impressions of Saurians and Tortoises, at Weston Point. Warwickshire and Staffordshire also were found to contain fossil footprints in their new red sandstone. A deposit of a similar age, although of a somewhat different nature, in America, was met with, having its beds impressed with the footprints of birds as well as reptiles. For a considerable time the new red sandstone was regarded as the only formation from which these impressions were obtained, but they are now procured from the lower portion of the coal-measures in America; and in this country the Devonian sandstone at Elgin shews fossil footsteps, and recently even the Potsdam sandstone, which appears to occupy a position equivalent to the Llandeilo flags, the base of the Silurian, has, in Canada, made us acquainted with the existence of reptile footprints at a period which is about the earliest from which we possess evidence of the existence of organised beings. With the exception of the impressions caused by birds found in America, the whole of the footprints are of such a nature as to indicate a relation to reptiles; and

amongst these we have representations of Chelonia, Sauria, and Batrachia, the three forms of reptile life, the only one wanting being Ophidia, which, from its structure, could not leave any traces of its former existence in the form of footsteps. With respect to the tracks which occur in the Potsdam sandstone, these shew their affinity to the steps of the Emydian family of Chelonia; and Professor Owen, from his examination of them, refers them to this form, both owing to the smaller size of the anterior extremities, and also from their legs appearing to have been of shorter length than those of land-tortoises. The fact of this animal having in some of the steps left traces of reticulation, and a groove which runs intermediate to the footprints of each side, leads to the conclusion that this chelonia was furnished with a projecting keel or plastron. Concerning the impressions found in the Devonian at Elgin, these seem to have been caused both by lizards and chelonia; and the occurrence of the Telerpeton Elginensis, a Lacertian form, which has left a portion of its structure in the sandstone of this locality, places us in possession of the oldest remains, except footprints, which have yet been discovered of vertebrata. The impressions which occur in the carboniferous rocks have, in general, a Batrachian character. In the coal-measures of Bavaria there have been obtained skeletons of reptiles, and some of these, according to Herman Von Meyer, "were provided with hands and feet, terminating in distinct toes; but these limbs were weak, serving only for swimming or creeping." This anatomist shews that these reptiles have some analogy to the Proteus anguinus, a reptile at the present time inhabiting subterranean lakes. It is, however, in the trias, the base of the secondary division of the geological formations, that we have the most abundant evidence of the former existence of reptile life, as left by their footprints. In this formation they occur in the greatest plenty in the Variegated sandstone (or Bunter sandstein), which forms the lowest portion of the trias.*

*We prefer the name Variegated Sandstone to the German one, Bunter sandstein.-EDIT.

Whether their great abundance here be owing to this deposit being of a nature more capable of receiving and retaining impressions, or to reptilian life prevailing to a greater extent during this period, or to the sandy nature of this deposit forming a suitable habitat, is a question which yet remains to be answered. In this formation, however, many and various forms of reptiles have left their tracks, and these tracks are in a much better state of preservation than those which the other formations afford.

Variegated sandstone, from whence the great bulk of the ichnolite markings are obtained, generally affords them in two conditions; one in which they are seen on the upper surface of the sandstone strata, and consisting of depressed markings, and the other when they occur in the under side of the stony layers, in which case the footprints are in relief, and form natural casts of impressions, commonly from a clayey deposit, which is usually too thin to be removed perfect from its original bed. The character of these impressions, so far as their perfection is concerned, depends in great measure upon the nature of the substance receiving the footstep, as well as upon the action of the water transporting the sandy matter which covers up and overlies the strata containing the impressions. When the animal has traversed a dry, sandy shore, we have the footprints distinct, so far as order and succession go, but, owing to the yielding sand trickling into the impressions as soon as the foot which caused them had been withdrawn, these tracks rarely present that sharp and definite outline which would enable a satisfactory conclusion to be drawn from them, concerning the form and nature of the animal to which they owe their origin. If the nature of the substance over which the animal walked was originally in a state approaching to quicksand, from its being saturated with water, then the character of the impression has been greatly modified. Under these circumstances, it usually happens that the marks of the forefeet have been obliterated, while the hinder ones consist of a series of steps, with a rounded outline in front, and gradually becoming shallower behind, until they are each about the level of the face of the stratum receiving the impression, and the back-part of the footprint is commonly lost sight of.

The absence of the impress of the fore-feet in beds which have originally been saturated with water, appears to arise from the circumstance that these animals in their progression caused their hinder extremities to form a deeper impress than the fore ones; and this affords another proof of the universality of the laws of nature, not only so far as present existing races are concerned, but likewise during periods long antecedent to the present order of things; for it is a fact that all walking animals have their posterior extremities so organised that in them shall reside to the greatest extent the power of progressive motion. The impressions are usually found in the most beautiful state of preservation when they occur either on the surface of a bed which contains a small portion of clay in its composition, or on a thin deposit of clay itself. When either of these is the case, the impress of each pair of feet is distinctly seen, shewing the form and arrangement of the toes or claws, and the hinder pair of steps are generally more perfect than the fore ones, which have often become partially obliterated by the hind feet treading upon the impressions caused by the fore ones. The reason why the footprints in this substance are in so perfect a state, is owing to the clay preventing the sand from falling into the impressions, and the nature of the matrix receiving the steps is such as to afford a soil sufficiently soft and yielding to receive a perfect impress, and, at the same time, sufficiently tenacious to retain all the fine traces left by the step after the foot had been withdrawn from the impression. The circumstances attendant on the occurrence of footprints when they are met with in this matrix, are such aspear most favourable to the perfection of impressions.

The Ufferent states of preservation in which the impressions occur,furnish us with important information concerning the nature and condition of the surface over which the reptiles passed. In the imperfect traces which are found, not only on the surfaces of some of the strata, but also in the interior of the stone when this is split along the lamina of its bedding, we have evidence of a soft sand not cohesive enough to retain distinct forms of footprints. In those impressions which have a rounded outline, we see a surface which at one time was yielding and tremulous, representing

the quicksands of our modern shores. And in the clayey deposits we find the action of quiet water, such as at the present time causes the muddy silt which occurs scattered in patches along a sandy coast. Such conditions and such results now prevail between tidal levels; and such conditions and such results have prevailed, under similar circumstances, along the ancient shores of the sea, long prior to anything to which our ideas can attach when we talk of antiquity-conditions which appear to be almost contemporaneous with the existence of animal life.

Concerning the animals which have produced these ichnolite tracks, they seem to have been not only of different forms, but likewise to have been of various natures, according as they existed during the periods when the trias was being deposited. Those impressions which first attracted attention have been assigned by Professor Owen to Chelonia, and, from the equal size of the pairs of feet he refers these footprints to Testudiniæ, rather than to Trionicideæ, the other two forms of tortoises which might have been supposed to produce impressions. These steps, which occur in great abundance in the quarry of Corncockle Muir, Dumfriesshire, have been distinguished by the name of Testudo Duncani; but as the generic appellation is used to designate the existing forms of land-tortoises, Sir Williain Jardine has substituted in its place the name Chelichnus. The same locality which furnishes the impressions of the C. Duncani, also affords another form somewhat allied to this species; but the steps being of much more gigantic proportions, this form has been termed C. giganteus by Sir William Jardine, and its specific characters are such as at once to separate it from the small species. Other reptilian forms of footprints are obtained from this quarry: there is, however, considerable difficulty in making out the relation which these form of steps bear to existing families; but in other parts of Dumfriesshire there occur associated with the impressions of the Chelichnus tracks of both Lacertian and Batrachian animals, and these appear to occupy a position similar to those which are found at Corncockle Muir.

These Lacertian and Batrachian impressions from the trias of Dumfriesshire differ in some respects from those