« 이전계속 »
geologists themselves maintain,1 these stratified formations are not new productions, in the sense that they were added from outside to the parts of the earth which already existed; they have existed as portions of the earth ever since the beginning of the creation, but in different places, and sometimes under different forms, and have only been displaced and transformed by various agents, of which water was one of the principal. Lime, sand, clay, etc., were carried by water from one place to another just as they are now; many minerals were dissolved in water, and were then deposited in various places and in various combinations, when they again hardened. The bulk of the earth has therefore not increased, nor has its crust become thicker on the whole by the formation of these strata, but there has been a removal of matter from one place to another, and a partial transformation of the same from one condition to another.
At this period of the earth's history, for which geologists rightly claim a greater amount of certainty than for the "mythical period," with which we have been occupied to-day,2 that science, which is a branch of geology and a help to it, and which, under the name of Palaeontology, has been cultivated in our day with special zeal and success, comes into prominence.
1 Burmeister, Gesch. der Schiipfung. p. 271.
The name of Fossils is given to those organic bodies of animals and plants, or to separate portions of them, which are found buried in the strata of the earth's crust, generally in a more or less altered condition.1 The name Petrifactions, which was formerly in use, does not apply to those organic bodies which have been preserved entire, with the original proportions of their elementary parts, such as the insects and parts of plants which we find enclosed in amber or rock-salt, and the bodies of mammoths, which have been dug out of the ice in Siberia in a perfectly undecayed condition.2 But these cases are rare; generally the softer parts of the bodies of the animals and plants which were enclosed in the hardening masses of the strata were dissolved or destroyed, or else they decayed, and as a rule only the firmer and harder portions of the organisms have been well preserved; especially the stems, branches, and hard fruits of plants; the bones, scales, teeth, horns, and shells of animals.
i The following observations are principally taken from Noggerath, Gea. Naturwiss, iii. p. 166; and Leonhard, Geol. i. p. 342. Fraas, lor der Siindjluth, p. 56. Cf. Zittel, Aiu der Urzeit, and his treatise, "Beitrage zur Geschichte der Palaontologie," in the Historischer Tatchenbuch, 5 Jahrg. (1875) pp. 139-180.
* Bulletin de VAcademie de St. Petersbcurg, xvi 147.
Many organic bodies, especially those of plants, have become carbonized, and changed into peat or coal. Others, especially the bodies of animals, have been lixiviated and disintegrated; that is, they have lost their gelatinous and other animal substances by gradual destruction and lixiviation, and in this altered and calcined state their colour, hardness, and weight have more or less disappeared. Other organic bodies again have been covered or surrounded, or encrusted as it is technically called, by mineral substances, as, for instance, calcareous tufa, which were originally fluid, and then hardened. But the real petrifaction occurs when an organic body is entirely changed into a mineral substance and still retains its original form. The solid parts of an organic body are, as is well known, porous; the pores are filled up by the minerals which are dissolved in water, and the substance of the organic body is by degrees chemically removed; the mineral substance replaces it, and gradually hardens; so that at last the organic substances have made way for mineral substances without producing any important change in the original form.
Sometimes an organic body, which after being entirely dissolved has been washed away and has disappeared, has left the impression of its outward form on the surrounding mineral rocks. Stems of trees, for instance, enclosed in some rock, have decayed in this manner, and their component parts have been entirely carried away; in their place a hollow space has been left, which has been filled up by some mineral substance, and this has taken the form of the original tree.1
1 "Some years ago I had to make an inquiry into the nature of some
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 Caiues of the Phenomena of Organic Nature, p. 45.
1 Cf. Quarterly Review, vol. ex. p. 109. Lyell, Geology, ii. 86, 100, 173. Fraas, Vor der Sundfluth, p. 224. Pfaff, Grundriss, pp. 293, 30f.
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.
We find even among the ancients occasional allusions to fossils.2 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,
1 On the other hand, another class of such impressions, the so-called fossil raindrops, do not seem to be authentic. (Fraas, Op. tit. 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 primaeval 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 Beptilion, 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."
* Quenstedt, Sonst und Jetzt, p. 195. E. V. Lasaulx, Die Geologie der Griechen und Etimer, Munich 1851, p. 4.