There are next to no pine trees in Denmark now, and it is apparently long since pine forests existed there; at least we have no historical records of their existence. But a careful examination of the peat moors there shows that pines did formerly exist in Denmark. There are, besides the ordinary meadow bogs which are formed in and round the river basins in the damp low parts of the valleys, and the high bogs which are formed from mosses in the plains, peculiar little forest bogs, skovmoose," which fill up deep hollows which have formed in the ground from various causes. Trees grew on the steep sides of these almost funnel-shaped hollows, and they gradually sank down and fell into the bogs. We find at the bottom of these bogs pines up to three feet thick, and sometimes, it is said, with several hundred rings; then evergreen oaks and hollies, which have also almost entirely disappeared from Denmark now; and then in the top layers, we come at last to oaks, birch, hazelnut, and alders. The beech, which now forms the Danish forests, is never found in the peat moors. So that it really seems as if we could distinguish in Denmark a pine, oak, and beech age. But will this enable us to determine the antiquity of the population of Denmark? Lyell says, "What may be the antiquity of the earliest human remains preserved in the Danish peat cannot be estimated in centuries with any approach to accuracy. .. In the time of the Romans the Danish isles were covered, as now, with magnificent beech forests. . . . Yet in the antecedent bronze period there were no beech trees, or at most but a few stragglers, the country being then covered with oak. In the age

of stone, again, the Scotch fir prevailed, and already there were human inhabitants in those old pine forests. How many generations of each species of tree flourished in succession before the pine was supplanted by the oak, and the oak by the beech, can be but vaguely conjectured, but the minimum of time required for the formation of so much peat must, according to the estimate of Steenstrup and other good authorities, have amounted to at least 4000 years; and there is nothing in the observed rate of the growth of peat opposed to the conclusion that the number of centuries may have been four times as great.'

" 1

Let us put aside the very doubtful attempt to identify the pine, oak, and beech ages with the ages of stone, bronze, and iron, and let us keep to the question of whether peat can be used here and in other places as a measure of time; whether by its aid we shall be able to determine the antiquity of the human race. This will only be possible if we assume beforehand that we know how quickly peat grows. If, for instance, we know that a peat bed increases by the thickness of 1 foot in 100 years, as it has been supposed to do on an average, we could say that 3000 years would be necessary for the formation of a peat bed 30 feet thick, such as is found often in Denmark. This would be a

2

simple calculation. But the matter is by no means

so easy.

Boucher de Perthes thought that peat increased at the rate only of 3 centimetres, that is, a good inch, in a century. But if this is so, a bed 30 feet thick

1 Antiquity of Man, p. 17.

2 Oswald Heer. See Vogt, Vorlesungen, ii. 95.

would require such myriads of years for its formation that even Lyell says he hesitates to accept this chronometric scale.' But on what does Boucher rest his calculations? In French peat beds Roman antiquities are found which must be 1500 years old. But the depth at which they occur, and the thickness of the peat beds which lie over them, vary very much in different places. This must necessarily be the case. Sometimes the peat is so liquid that heavy objects sink into it, sometimes so tough and dense that they remain on the surface. Now Boucher found several flat earthen plates of Roman make in one place lying horizontally, so that they could not have sunk in far, and on this he based his calculation. But it is most arbitrary to draw a general inference from one single instance, and Lyell observes quite rightly that data for determining the age of peat beds can only be obtained by multiplying such observations and carefully comparing them. He adds that up to that time no careful observations had been made in order to determine what is the minimum time which is requisite for the formation of a certain amount of peat. Vogt speaks even more decidedly if possible about this subject on two occasions. "Up to the present time we have no data for determining the rate at which peat grows, for the calculations which people have tried to make rest on very uncertain foundations. There are no materials at present for calculating the vertical increase of peat; and after a great deal of correspondence and conversation with the men who are trying to determine it, I have not arrived at any single fact which would make the calculation easier." "

1 Antiquity of Man, p. 156.

2 Vorlesungen, ii. 131, 153.

But if, as Vogt says, "a science which is to draw irrefutable conclusions must have mathematically certain premises," it is clear that no calculation ought to be attempted so long as those premises are absent. There is not even an immediate prospect of obtaining such premises, for all kinds of things have to be considered in calculating the growth of peat. Lyell says that peat-cutters tell him that they have never known any of the holes made in the peat to fill up; therefore they thought that peat did not grow at all. He adds that is not the case, but that it shows that the growth is very slow. Others say that in the East Frisian plains, ditches 6 feet deep grow up again in thirty years; the peat is not of a very dense texture, but it may be obtained several times. Were we

to found a calculation on this instance alone, we should find that the age of a peat bed of 30 feet, which Boucher de Perthes reckons at 30,000 years, was 200. Both calculations are undoubtedly wrong.

"One foot in thickness of highly compressed peat, such as is sometimes reached in the bottom of the bogs, is," as Lyell says, "obviously the equivalent of a much greater thickness of peat of spongy and loose texture, such as is found near the surface." Farther on he observes: "Differences in the humidity of the climate, or in the intensity and duration of summer's heat and

1 Vorlesungen, i. 4.!

2 Leonhard, Geologie, iii. 534. Quenstedt, Epochen, p. 793. Lesquereux has shown that in the Jura peat seldom grows less than 2 feet in a century, and may grow twice as much. He quotes one instance which shows that after the peat had been cut, new peat 6 feet deep formed in one place in 70 years, while in another place only 4 feet formed in 140 years In other places it has grown even faster, in one instance from 4 to 6 feet in 30 years.-Nöggerath, Der Torf, Berlin 1875, p. 16.

winter's cold, as well as diversity in the species of plants which most abound, would cause the peat to grow more or less rapidly, not only when we compare two distinct countries in Europe, but the same country at two successive periods.'

Even in the same country peat will grow in the same time, in one place 1 foot and in another 1 inch. It depends on the condition of the ground, and on the plants which occur in it. Some peat mosses in Scotland, described by Hugh Miller,' only date from Roman times; not only have quantities of Roman coins and other ancient remains been found there, e.g. a Roman kettle 8 feet under the surface, but also Roman axes sticking in the trees which are buried in the peat. Apparently the Roman soldiers cut their way here through forests; the trees they cut down decayed on the ground, dammed up little brooks, and so formed pools; the ground, deprived of air and light, could not support its former vegetation; thus watery, mossy bogs were formed, one generation flourished and decayed after another, and in the course of time a deep peat moss was formed.

Lyell himself in one of his earlier works has put together a series of facts which are unfavourable to the theory of a general very slow growth of peat: "In the

1 Antiquity of Man, p. 156. Nöggerath, Op. cit.: "If the conditions under which peat can be formed are absent, for instance if there is no water and the moss dries up, the growth stops. No doubt the growth of peat did stop on some of the old moors in ancient times for this reason, on others it may only have been interrupted for several centuries. Thus Cuvier was justified in asserting that the growth of peat could not be used as a measure of time in order to estimate the antiquity of the present condition of the earth's surface."

2 Sketchbook, p. 7.