The fossil impressions or footprints of animals, "Ichnites or Ichnolites," belong to this class. An animal passing over the surface of a bed of clay which had not yet hardened, left the impression of its feet marked in it. After the bed of clay had hardened, with the marks of these impressions, a new layer was formed above it which filled up the impressions, so that we now find the imprints of the feet engraven in the lower layer and in relief in the upper. These fossil footprints were first observed about fifty years ago by a Scotch clergyman, Dr. Duncan ;1 and since then they have frequently been found. The animal to which these footprints have been ascribed has been named Cheirotherium or hand animal, because the impressions distantly resemble the stamp of a man's hand. It seems certain that these impressions were really made by animals, and did not originate in any other way. As I have said, many impressions have been found, and they have been found in rows, one behind the other, so that the size of the step can

very curious fossils sent to me from the north of Scotland; a series of holes in some pieces of rock, and nothing more. These holes, however,

had a certain definite shape about them, and when I got a skilful workman to make castings of the interior of these holes, I found that they were the impression of the joints of a backbone, and of the armour of a great reptile, twelve or more feet long. This great beast had died, and got buried in the sand; the sand had gradually hardened over the bones, but remained porous. Water had trickled through it, and that water being probably charged with a superfluity of carbonic acid, had dissolved all the phosphate and carbonate of lime, and the bones themselves had thus decayed and entirely disappeared; but as the sandstone happened to have consolidated by that time, the precise shape of the bones was retained."-Huxley, On our Knowlege of the Causes of the Phenomena of Organic Nature, p. 45.

1 Cf. Quarterly Review, vol. cx. p. 109. 173. Fraas, Vor der Sündfluth, p. 224.

Lyell, Geology, ii. 86, 100, Pfaff, Grundriss, pp. 293, 305.

be ascertained; and in four-footed animals, the print of the hind feet can be distinguished from that of the fore feet.1

This, and much more, is now to be found in every handbook of natural science which treats of fossils. But on this, as on other points, science has only arrived at clear and certain knowledge after long search and many errors; and now that our knowledge of fossils is complete, at least in its principal parts, it will not be uninteresting to look back on the road which, not always in a straight direction, but with many zigzags, has led to this knowledge.

2

We find even among the ancients occasional allusions to fossils. It is said that in the year 540 B.C. the philosopher Xenophanes of Colophon inferred from the remains of fish and other sea animals which were found in quarries near Syracuse, that the surface of the earth must at one time have been in a slime-like condition,

On the other hand, another class of such impressions, the so-called fossil raindrops, do not seem to be authentic. (Fraas, Op. cit. p. 169; Zittel, Aus der Urzeit, p. 258.) Small rounded impressions are sometimes found in sandstone strata, and, on the overlying stratum, corresponding rounded formations in relief. It has been thought that these impressions were produced by falling raindrops, from rain which fell in primæval times when the sandstone was beginning to harden. In one case it was thought that it could be discovered from which direction the rain came, because the sides of the impressions are rather elevated on one side, just as would be the case if rain driving sideways were to fall on one of our sandy shores. But Vogt says (in one of the notes to the Vestiges of the Natural History of Creation, p. 74; cf. H. V. Meyer, Ueber die Reptilion, p. 142), "The impressions have been recently much more probably explained, by the action of the atmosphere on the cement of the sandstone, or by air bubbles left on the surface of the sand which was covered with the waves. This superficial change takes place sooner or later in most sandstones, according to the quality of the cement."

2 Quenstedt, Sonst und Jetzt, p. 195. E. V. Lasaulx, Die Geologie der Griechen und Römer, Munich 1851, p. 4.

R

and have formed a sea-bed. The sea-shells found on mountains, or in other places far from the sea, were especially noticed by the ancients; they connected them, as we know from Ovid,' with the traditions of an ancient flooding of the earth, and it was very natural therefore that Tertullian should have supposed that they were left by the Deluge.2

The ancients were no doubt right in imagining that the fossils come from organic beings, and that they were caused and deposited by the agency of water. It is strange that these two simple truths should have been neglected by so many, when people first began to turn their attention to mineralogy and geology a few centuries ago. Many scientific men in the 16th and 17th centuries thought that fossils had no connection with the remains of plants and animals, but were pure mineral forms, like crystals and stalactites. Their resemblance to shells, bones, and stems of trees was supposed to be accidental, just as stalactites, pebbles which have been rubbed together by the action of water, and the weather-beaten points of rocks often assume all kinds of curious shapes. Fossils were usually called lusus naturæ by this class of scientific men. One of them, the famous Athanasius Kircher, says: "As sportive nature cannot give the power of vegetation and sensation to the mineral world, she has done what she could; for as she could not give life and

1 Metam. xv. 262.

2 Tert. de pallio, c. 2: Mutavit et totus orbis aliquando aquis omnibus obsitus; adhuc maris concha et buccinæ peregrinantur in montibus, cupientibus Platoni probare etiam ardua fluitasse. Isid. Etymol. xiii. 22 : Cujus (diluvii) hactenus indicium videmus in lapidibus, quæ in remotis montibus conchis et ostreis concretos, sæpe etiam cavatos aquis visere solemus. Cf. Lasaulx, Op. cit. p. 14.

feeling to the stones, she has at any rate given to them the form of animals and plants."1

2

The most adventurous, and sometimes superstitious, conjectures were then made in order further to explain the existence of the fossils: these shapes of stones had sometimes been caused by the influence of the planets; sometimes by an aura seminalis, a seed vapour; sometimes by a demon working in the depths of the earth; the more reasonable restricted themselves to the supposition that they were simply the result of a vis plastica, a creative force of nature. Many went so far in this theory as to apply it in the most ridiculous way. An Italian doctor declared the potsherds which are found heaped up in the Monte Testaccio in Rome, and which are undoubtedly of human fabrication, to be lusus naturæ. The Stuttgard doctor Lentilius, in the year 1709, insisted on it that shells hardly differing from those now washed up on the shores of the Lake of Constance were lusus naturæ. In 1696 the skeleton of a mammoth was found at Burgtonna; the Collegium medicum, when they were asked their opinion on it by the Duke of Gotha, declared it to be a lusus naturæ; no one but the ducal librarian Tentzel was unprejudiced enough to believe that the bones were real.3

This theory had its supporters in all countries during the 16th and 17th centuries. One of the last and

1 Mundus subterraneus (1664), ii. 27; see Quenstedt, Sonst und Jetzt,

2 Wiseman, On the Connection, etc., p. 249. Quenstedt, Sonst und Jetzt, p. 202. Lasaulx, Op. cit. p. 8. Fraas, Vor der Sündfluth, p. 414. Zittel, see the Hist. Taschenb. p. 146.

3 Wagner, Gesch. der Urwelt, ii. 386.

most unhappy was the Würzburg professor of medicine, Dr. Beringer. As dean of his Faculty, he published in the year 1726 a Latin treatise, with numerous drawings of some curious stones which he had found in a hill near Würzburg. In his introduction he expresses a hope that the land of Franconia would in future be as renowned for these unique stones as for its excellent wine. The stones, as drawn by him, no doubt have not their match in nature; they consist not only of shells, crabs, fish, etc., but also of bees and butterflies perched on flowers, cobwebs, honeycombs, pictures of the sun, the moon, and of comets with their tails; and also of Hebrew, Latin, and Arabic characters. Of course these could not be fossils, and, as Beringer proves at great length, they could not be supposed to be the work of the heathen Germans, because they did not understand Hebrew and Arabic; therefore they could only be lusus naturæ. The learned man does mention in the last pages of his book that there was some talk in the town, and especially over the bottle, of a trick which had been played him; but this idea he dismisses for several reasons, and he accuses two former colleagues of having spread these malicious reports. The facts were soon explained: some mischievous students had made these remarkable shapes out of plaster and clay, and had buried them in the place where the professor was accustomed to seek for fossils, or lusus naturæ. They were cruel enough to carry the jest so far as 'Lithographia Wirceburgensis ducentis lapidum figuratorum, a potiori insectiformium, prodigiosis imaginibus exornatæ specimen, quod . . . præside, J. B. A. Beringer, publicæ literatorum disquisitioni

submittit, G. L. Hueber, Wirceb. 1726, fol.