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IMPRESSIONS OF THE PAST

"The weird palimpsest, old and vast, Wherein thou hid'st the spectral past."

The Rev. H. N. Hutchinson commences one of his interesting books with Emerson's saying, "that Everything in nature is engaged in writing its own history;" and, as this remark cannot be improved on, it may well stand at the head of a chapter dealing with the footprints that the creatures of yore left on the sands of the sea-shore, the mud of a long-vanished lake bottom, or the shrunken bed of some water-course. Not only have creatures that walked left a record of their progress, but the worms that burrowed in the sand, the shell-fish that trailed over the mud when the tide was low, the stranded crab as he scuttled back to the sea—each and all left some mark to tell of their former presence. Even the rain that fell and the very wind that blew sometimes recorded the direction whence they came, and we may read in the rocks, also, accounts of freshets sweeping down with turbid waters, and of long periods of drouth, when the land was parched and lakes and rivers shrank beneath the burning sun.

All these things have been told and retold; but, as there are many who have not read Mr. Hutchinson's books and to whom Buckland is quite unknown, it may be excusable to add something to what has already been said in the first chapter of these impressions of the past.

The very earliest suggestion we have of the presence of animal life upon this globe is in the form of certain long dark streaks below the Cambrian of England, considered to be traces of the burrows of worms that were filled with fine mud, and while this interpretation may be wrong there is, on the other hand, no reason why it may not be correct. Plant and animal life must have had very lowly beginnings, and it is not at all probable that we shall find any trace of the simple and minute forms with which they started,[2] though we should not be surprised at finding hints of the presence of living creatures below the strata in which their remains are actually known to occur.

[2] Within the last few years what are believed to be indications of bacteria have been described from carboniferous rocks. Naturally such announcements must be accepted with great caution, for while there is no reason why this may not be true, it is much more probable that definite evidence of the effects of bacteria on plants should be found than that these simple, single-celled organisms should themselves have been detected.

Worm burrows, to be sure, are hardly footprints, but tracks are found in Cambrian rocks just above the strata in which the supposed burrows occur, and from that time onward there are tracks a-plenty, for they have been made, wherever the conditions were favorable, ever since animals began to walk. All that was needed was a medium in which impressions could be made and so filled that there was imperfect adhesion between mould and matrix. Thus we find them formed not only by the sea-shore, in sands alternately dry and covered, but by the river-side, in shallow water, or even on land where tracks might be left in soft or moist earth into which wind-driven dust or sand might lodge, or sand or mud be swept by the mimic flood caused by a thunder shower.

So there are tracks in strata of every age; at first those of invertebrates: after the worm burrows the curious complicated trails of animals believed to be akin to the king crab; broad, ribbed, ribbon-like paths ascribed to trilobites; then faint scratches of insects, and the shallow, palmed prints of salamanders, and the occasional slender sprawl of a lizard; then footprints, big and little, of the horde of Dinosaurs and, finally, miles above the Cambrian, marks of mammals. Sometimes, like the tracks of salamanders and reptiles in the carboniferous rocks of Pennsylvania and Kansas, these are all we have to tell of the existence of air-breathing animals. Again, as with the iguanodon, the foot to fit the track may be found in the same layer of rock, but this is not often the case.

Although footprints in the rocks must often have been seen, they seem to have attracted little or no notice from scientific men until about 1830 to 1835, when they were almost simultaneously described both in Europe and America; even then, it was some time before they were generally conceded to be actually the tracks of animals, but, like worm burrows and trails, were looked upon as the impressions of sea-weeds.

The now famous tracks in the "brown stone" of the Connecticut Valley seem to have first been seen by Pliny Moody in 1802, when he ploughed up a specimen on his farm, showing small imprints, which later on were popularly called the tracks of Noah's raven. The discovery passed without remark until in 1835 the footprints came under the observation of Dr. James Deane, who, in turn, called Professor Hitchcock's attention to them. The latter at once began a systematic study of these impressions, publishing his first account in 1836 and continuing his researches for many years, in the course of which he brought together the fine collection in Amherst College. At that time Dinosaurs were practically unknown, and it is not to be wondered at that these three-toed tracks, great and small, were almost universally believed to be those of birds. So it is greatly to the credit of Dr. Deane, who also studied these footprints, that he was led to suspect that they might have been made by other animals. This suspicion was partly caused by the occasional association of four and five-toed prints with the three-toed impressions, and partly by the rare occurrence of imprints showing the texture of the sole of the foot, which was quite different from that of any known bird.

Fig. 6.—Where a Dinosaur Sat Down.

In the light of our present knowledge we are able to read many things in these tracks that were formerly more or less obscure, and to see in them a complete verification of Dr. Deane's suspicion that they were not made by birds. We see clearly that the long tracks called Anomœpus, with their accompanying short fore feet, mark where some Dinosaur squatted down to rest or progressed slowly on all-fours, as does the kangaroo when feeding quietly;[3] and we interpret the curious heart-shaped depression sometimes seen back of the feet, not as the mark of a stubby tail, but as made by the ends of the slender pubes, bones that help form the hip-joints. Then, too, the mark of the inner, or short first, toe, is often very evident, although it was a long time before the bones of this toe were actually found, and many of the Dinosaurs now known to have four toes were supposed to have but three.

[3] It is to be noted that a leaping kangaroo touches the ground neither with his heel nor his tail, but that between jumps he rests momentarily on his toes only; hence impressions made by any creature that jumped like a kangaroo would be very short.

It seems strange, and it is strange, that while so many hundreds of tracks should have been found in the limited area exposed to view, so few bones have been found—our knowledge of the veritable animals that made the tracks being a blank. A few examples have, it is true, been found, but these are only a tithe of those known to have existed; while of the great animals that strode along the shore, leaving tracks fifteen inches long and a yard apart pressed deeply into the hard sand, not a bone remains. The probability is that the strata containing their bones lie out to sea, whither their bodies were carried by tides and currents, and that we may never see more than the few fragments that were scattered along the seaside.

That part of the Valley of the Connecticut wherein the footprints are found seems to have been a long, narrow estuary running southward from Turner's Falls, Mass., where the tracks are most abundant and most clear. The topography was such that this estuary was subject to sudden and great fluctuations of the water-level, large tracts of shore being now left dry to bake in the sun, and again covered by turbid water which deposited on the bottom a layer of mud. Over and over again this happened, forming layer upon layer of what is now stone, sometimes the lapse of time between the deposits being so short that the tracks of the big Dinosaurs extend through several sheets of stone; while again there was a period of drouth when the shore became so dry and firm as to retain but a single shallow impression.