III
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.