then fell into disuse, so that the deposits 64 feet deep which cover it may have been heaped up by the wind and the water. Others say that the hut was destroyed by the downfall of a sand-hill. At any rate it is not thousands of years old.1 These facts prove that the upheaval and depression of the ground is a very varying geological phenomenon which cannot be averaged, and that no distinct rule can be laid down about it which will hold good for all countries and all times. For just as now the upheaval and depression goes on in different countries under different conditions at different rates of progression, so it may have gone on more or less slowly in different centuries in the same country. If, then, it has been ascertained by observations made in this century that Sweden is rising at the rate of 2 or 4 feet in a hundred years, it does not follow that this gradual upheaval was not greater in former centuries; nor that besides this gradual rise, at some periods and in some places, a sudden rise may not have occurred. At any rate no trustworthy measure of time can be obtained by this means, and all calculations about the age of the implements and boats 2 1 Archiv für Anthr. vii. 276. Corr.-blatt der D. Gesellschaft für Anthr. 1875, p. 18. "The assertions of the recent Géologie Archéologique, in spite of their incomparable assurance, often lead us to suspect that the whole thing is a joke, and intended to mystify antiquaries. What are we to think of the fisherman's hut, with the hearthstone and the bundle of faggots on it, which was found near the Mäeler lake 64 feet deep in the earth, and which had been sinking so slowly and undisturbedly for 80,000 years at the rate of 10 inches a century, that hut, hearthstone, and faggots had, marvellous to say, escaped destruction?" See Lindenschmidt in the Archiv für Anthr. i. 53. Cf. O. Schmidt, Oesterr. Wochenschrift, 1863, ii. p. 388. Cotta, Geol. Bilder, p. 49. Pfaff, Die neuesten Forschungen, p. 71. found in Scotland and in Sweden, which are based on the rate at which land is rising, are no more than arbitrary assumptions, because the rate of progression is not sufficiently known, and can never be definitely ascertained. It is interesting to know what Lyell has said on this subject. "As no accurate observations on the rise of the Swedish coast refer to periods more remote than a century and a half from the present time, and as traditional information, and that derived from ancient buildings on the coast, do not enable the antiquary to trace back any monuments of change for more than five or six centuries, we cannot declare whether the rate of the upheaving force is uniform during very long periods. As the movement is now very different in different places, it may also have varied very much in intensity at different periods."1 In conclusion I will mention an analogous case, which clearly shows how little the changes in the proportion of land and sea can be of use to us as a measure of time. We know that the coast of Medoc in the Bay of Gascony is continually being encroached upon by the ocean. The ancient Noviomagus, which was swallowed up by the waves in the year 580 A.D., lies in ruins under the sea. The rock of Cordouan, on which was a lighthouse, was originally connected with the coast, it is now distant from it about three leagues. Since 1818 the rate at which the sea is encroaching has been accurately recorded. From 1818 to 1830 the sea gained 180 metres of ground. If we average this, we get 15 metres a year, and according to this the sea 1 Principles of Geology, ii. p. 345. Cf. Leonhard, Geologie, ii. 89. would have gained another 180 metres in twelve more years, that is, from 1830 to 1842. But it did not do this by any means, for instead of 180 metres it gained in those twelve years 350 metres, that is to say 29 instead of 15 metres a year, and from 1842 to 1845 it gained at the rate of 35 metres.' Who is to prove that the contrary may not have occurred in other instances of alterations in the face of the country, and that the alteration in former centuries was not much greater than in the last? The same holds good for the Niagara Falls, which have been used for measuring time. It has been observed that the Falls recede from 1 to 2 feet in each year, and it had been calculated that it took 35,000 years to form the gorge. Recent observations, however, show that latterly it has receded more than 3 feet in a year. Calculation is impossible, for it washes away both hard and soft strata, and nobody knows how great was the volume of water which came over the Falls 1000 years ago." 4. In the Somme valley, near Amiens and Abbeville, human bones and implements have been found in gravel beds which do not lie near the present river bed, but on the slope of the hills round the valley, and are from 80 to 100 feet higher than the present river bed. I have already mentioned the discovery, and I shall return to it shortly; at present I am only concerned to find out whether the age of these gravel deposits can be calculated. They are covered by a layer of sand of about 6 feet thick, by a layer of clay of the same thickness, and by a layer of common alluvial soil. 1 Ausland, 1862, 1032. See also Molloy, Geology, p. 47. These three layers have therefore been deposited still later than the gravel bed, and when this gravel bed was deposited the valley must have had a shape quite different from the present. Since the valley assumed its present shape, a peat bed has been formed in it, which is in places 30 feet deep.1 We shall see later that this peat bed gives us no data for calculating how long the valley of the Somme has existed in its present shape. But is it possible to calculate the length of time during which the valley was changed to its present shape from that which it had when the gravel bed was deposited? If we are to assume, with Lyell and Vogt, that the Somme has gradually hollowed out the valley until it formed its present bed, as it is supposed that some rivers slowly but continuously hollow out their beds, a very long time must of course have elapsed since the valley had such a conformation that the gravel bed was deposited by the river. Lyell himself suggests the objection, that if we judge by the alterations which are still going on in the river beds, no period of time would be long enough to explain such a transformation of the valley. To this he answers, that it is more than probable that such alterations, together with elevations and subsidences of the land, took place in former times more rapidly than they do now. But if we assume that formerly other and more powerful causes existed, or that the present causes worked with greater intensity, then surely we entirely give up all hope of calculating time. The only possible formula for such a calculation is this. "The river deepens its bed, accord1 Vogt, Vorlesungen, ii. p. 46 seq. ing to present observations, at the rate of-let us say— a foot a century; the conformation of the valley shows that the river bed lay formerly 100 feet higher than it is now, therefore since then 10,000 years have gone by. But the calculation is not correct, indeed any calculation becomes impossible directly we admit, what according to Lyell is "more than probable," that besides this deepening of the river bed at the rate of one foot a century, other causes may have been at work which have altered the conformation of the valley; such as, for instance, inroads of the sea, which, according to Vogt, has evidently sometimes penetrated far inland in the Somme valley, other inundations which may have removed masses of earth and stone, upheavals which have raised the sides of the river valley, or subsidences by which its centre has been lowered. I am, of course, not able to prove that such causes have really been at work to alter the configuration of the Somme valley in the course of about 4000 years; I am not even enough of a geologist to describe in detail the occurrences by which this alteration may possibly have been produced in this time. But in order to be persuaded that nothing here compels us to put the antiquity of man many myriads of years back, it is quite enough for us laymen to know first, that Lyell himself refrains. from making any estimate, because he admits that it is possible, and even highly probable, that other forces may have been at work here formerly besides the river with its slow washing away of the soil; and secondly, that other geologists think that it is probable that the conformation of the valley has altered in a shorter |