centre, but that all round the outside it was petrified to the thickness of half an inch, and changed into agate. As it was known that this trunk had been in the Danube for 1700 years, it was easy to calculate that a period of at least 2-300,000 years would have been necessary for the complete petrifaction of trunks such as have been found of from six to eight feet thick. The calculation would be infallibly correct had it not been proved that under some circumstances petrification takes place much more quickly than it did in the case of the supports of the bridge. Petrified logs of wood have been found in America which had evidently been hewn by European axes, and which therefore had gone through the process of petrification in a few centuries. In Westphalia pebbles and flints have been found, for whose formation geologists would suppose that some thousands of years were necessary, were it not for the fact that when they were split open coins were found which bore the stamp and the date of the coins of the Bishops of Munster, and therefore belonged to the sixteenth and seventeenth centuries.1 A stream of lava, which flowed from Etna in the time of Thucydides, still lies bare and sterile, with hardly a sign of soil or vegetation. Therefore it takes at least 2000 years before a stream of lava can be covered with fertile earth and plants. If, therefore, we 1 For similar examples, see Molloy, Geology, p. 84. In 1832 thousands of silver coins, belonging partly to the thirteenth and fourteenth centuries, were found in the bed of the Dove, in Derbyshire, buried ten feet below the surface in a hard conglomerate. In the beginning of this century a ship was wrecked near Cape Frio, in Brazil; a few months later the dollars and other valuables which were on board on being sought for were found imbedded in hard quartz-like sandstone. In the museum at Montpellier there may be seen a cannon, enclosed in crystalline limestone, which was found near the mouth of the Rhone in the Mediterranean. find ten such lava streams, one above the other, all covered on the surface with fertile earth, it shows that the volcano must have been active 20,000 years ago. The calculation is very simple, but it is incorrect. Herculaneum was destroyed 1800 years ago, and is already covered with six such alternating layers of lava and fertile earth; and many of the streams of lava which have issued from Vesuvius and Etna within the memory of man are already fitted for cultivation. Only a few years ago ruins were excavated near Wroxeter which, with the exception of a small bit of wall, were all covered with a thick layer of earth. Judging by the thickness of these layers, geologists would probably have supposed that these ruins were several thousand years old, but for the facts that Roman coins of the fourth century A.D. have been found there, and that we know from history that in the Roman times this was the site of Uriconium. It has been rightly observed in connection with this in England, that in the case of abbeys which were destroyed only 300 years ago, the earth has been already heaped up to a considerable height.' The following facts, quoted by O. Fraas,' show us how little suited the formations of tufa and other watery deposits are for chronological calculations. "In the old Greek watering-place Aidepsos, which was world-renowned even in the time of Sulla, the old Roman baths were dug out from under many yards of calcareous tufa; and when the new baths at 1 Ausland, 1864, p. 399. 2 Die alten Höhlenbewohner, Berlin 1873, p. 29. Baden Baden were made, they found, deep below the surface, skilfully worked baths dating from the Roman time. Here, therefore, the waters have in the course of sixteen to eighteen centuries accidentally deposited a mass of stone on the surface of the earth; while close by there are human remains of the same period, if not earlier, which are hardly covered by the grass. Karl Vogt admits, without hesitation, that the thickness of the stalagmite deposits which cover the remains of men and extinct animals in the bone caves, gives no evidence as to the time which was necessary for their formation, and therefore is no criterion of the age of those remains. "The deposit varies to a great extent, sometimes in a remarkable degree in the same caves, according to the quantity of trickling water and to the quality and solubility of the lime.' "Who would venture to assert certainly," says Schaaffhausen, "that the covering of stalagmite on the bones of the cave bears is more than 2000 years old? And yet these formations in the Kent caves have been supposed to be 210,000 years old. It has been asserted on trustworthy authority that in a tunnel driven through limestone hills, stalactites 4 inches long and inch thick have been formed in the course of nine months." 2 Nor can the condition of the bones give us any definite information about their age. "In bone caves where the covering of stalagmite was absent," says Vogt," and where the soil was quite dry, the bones 1 Vorlesungen, ii. 8. 2 Archiv für Anthropologie, v. 119. Cf. same, viii. 270. often mouldered away to such an extent that when they were touched they turned to dust; in those cases where the covering of stalagmite exists they are generally in a much better state of preservation." Formerly it was thought that "fossil" bones could be distinguished from recent bones, because the former stick to the tongue and the latter do not. Bones stick to the tongue because they have lost the organic cartilage; but the rapidity with which this takes place depends on various circumstances. Nor do other differences, which have been observed in examining old bones microscopically and chemically, give us any data for ascertaining their age. For if we succeeded in ascertaining what is the process of the gradual decomposition of the bones under certain circumstances and conditions, we could only deduce from it a universal rule for defining their age if we could assume that the conditions and circumstances have always and everywhere been the same. But we cannot assume this, because the contrary is undoubtedly the case.1 These observations will show how uncertain are the means geology possesses for ascertaining the antiquity of the human race. The fact that now after which were made with a few years many assertions great confidence at the beginning of these inquiries are acknowledged to be untenable, is an agreeable proof of the real progress of inquiry. It often happens that when a new subject is brought up for discussion, there is a general belief that the discoveries which have been made will warrant our asserting certain things as assured facts; but then with time, not only do the 1 Archiv für Anthropologie, v. 114, viii. 3. materials which have to be considered increase, but criticism becomes sharper, and consequently much which was formerly believed to be indisputable becomes uncertain, and much is proved on nearer examination to be untenable. It needs, I think, no prophet to foresee that in a few years it will be generally acknowledged that all attempts to calculate directly the antiquity of man by means of geology cannot lead to a conclusion at all certain. I shall speak on another occasion more particularly of the indirect means. To-day I will discuss in detail a few calculations of the kind I have described, which are already acknowledged to be untenable by savants, but are still employed by amateurs, simply because they produce the most remarkable results. 1. Leonard Horner made the following calculation. The base of the colossal statue of Ramses II., at Memphis, which, according to Lepsius, was erected in the year 1360 B.C., is now covered with Nile sediment to a height of 9 feet 4 inches; therefore the Nile has deposited a layer 3 inches thick in a century. Now in sinking wells and in boring in different places, and at different depths, only remains of still existing kinds of animals have been found; and at no less a depth than 39 feet, fragments of an earthen vessel,—still deeper, bricks have been found. According to the calculation given above, it would take thus more than 12,000 years to form the deposit 39 feet in thickness, which covered the fragments. Now, apart from other considerations, the following objection may be made to this calculation. Horner supposes that the deposit 1 1 Ebers, Ægypten und die Bücher Moses, 1 Bd. Leipzig 1868, p. 21. |