Chapter XIX.

The perfect preservation of so many fossil remains of animals and plants, which enables us to trace the progress of organic life on earth from one vast epoch to another, is surely wonderful enough; but we must consider it as a still greater wonder that phenomena usually so evanescent as foot-prints, ripple-marks, and rain-prints should in some cases have been permanently engraved in stone, and appear as distinct after millions of years as if their traces had been left but yesterday. All these marks were at first printed on soft argillaceous mud, on the sea-shore, or on the borders of lakes and rivers, which retained them as they became dry. Sand or clay having then been drifted into the mould by the wind, or deposited in its cavity by the next tide, a permanent cast was made, indented in the lower stratum and standing out in relief on the upper one.

Thus rain-drops on greenish slates of the Coal period, with several worm tracks, such as usually accompany rain-marks on the recent mud of modern beaches, have been discovered near Sydney, in Cape Breton. As the drops resemble in their average size those which now fall from the clouds, we may presume that the atmosphere of the Carboniferous period corresponded in density with that now investing the globe, and that different currents of air varied then as now in temperature, so as, by their mixture, to give rise to the condensation of aqueous vapour.

In like manner it has been possible to detect the footprints of reptiles, even in shales as old as the Cambrian formation, and to follow their trail as they walked or crawled along.

In the Upper New Red Sandstone (Lower Trias), near Hildburghausen, in Saxony, a strange unknown animal, supposed to belong to the frog order, has left foot-prints bearing a striking resemblance to the impressions made by a human hand; and in the still older red sandstone of Connecticut, a gigantic bird has marked a foot four times larger than that of the ostrich. It existed long before the Ichthyosaurus was seen on earth, and yet by a singular chance its traces, printed on a foundation proverbially unstable, have outlived the wreck of so many ages.

However brief and defective the foregoing review of the fossil world may have been, it has still sufficed to point out the existence on our planet of so many habitable surfaces, each distinct in time, and peopled with its peculiar races of aquatic and terrestrial beings, all admirably fitted for the new states of the globe as they arose, or they would not have increased and multiplied and endured for indefinite periods.

‘The proofs now accumulated,’ says Sir Charles Lyell, ‘of the close analogy between extinct and recent species are such as to leave no doubt on the mind that the same harmony of parts and beauty of contrivance which we admire in the living creation has equally characterised the organic world at remote periods. Thus, as we increase our knowledge of the inexhaustible variety displayed in living nature, our admiration is multiplied by the reflection that it is only the last of a great series of pre-existing creations, of which we cannot estimate the number or limit in times past.’