15 



" This tree is not now, nor has ever been in historical times, a native of the 

 Danish islands, and when introduced there it has never thriven ; yet it was 

 evidently indigenous in the human period, for Steenstrup has taken out with 

 his own hands a flint instrument from below a buried trunk of one of these 

 pines. It appears clear that the same Scotch fir was afterwards supplanted by 

 the sessile variety of the common oak, of which many prostrate trunks occur in 

 the peat at higher levels than the pine ; and still higher the pedunculated 

 variety of the same oak (Q'tercus robur, L.) occurs with the alder, birch 

 (Betula verrucosa, Ehrh.), and hazel. The oak has now in its turn been 

 almost superseded in Denmark by the common beech. Other trees, such as 

 the white birch (Betula alba), characterize the lower part of the bogs, and 

 disappear from the higher; while others again, like the aspen (Populus 

 tre,mula\ occur at all levels, and still flourish in Denmark." 



From Vaupell's Bogens Indvandring we learn some curious 

 results in regard to what may be called the natural succession of forest 

 trees, which have been obtained in the examination of the bogs of 

 Denmark by Steenstrup and himself. The bogs appear to have gone 

 through some gradual process of desiccation ; and the birch, which 

 grows freely in very wet soils, appears to have contributed very 

 effectually by its annual deposits to raise the surface above the water 

 level, " and thus," says Marsh, " to prepare the ground for the 

 oaks." 



Between the extremes referred to as characteristic of the state of the 

 ground in these peat bogs when the first and when the last of the 

 trees borne by it appeared, there are innumerable gradations, and by 

 the student of the habitats of different trees something may be learned 

 in regard to what is the character of the soil in regard to humidity or 

 aridity from the species produced by it. 



In a volume entitled " Forest Moisture ; or, the Effects of Forests 

 in Humidity of Climate," * I have given details illustrative of the 

 drying up of marshes on the growth of trees, and of the desiccating 

 effects produced in marshes by forests in prolonged periods; and 

 reference is here made to the indications supplied by successive crops 

 of different kinds of trees of the progress of such operations. 



From Bogens Indvandring i de Danske Shove, by Chr. Vaupell, we 

 learn that within thirty years these bogs have yielded above a million 

 of trunks of trees, and that they are found in depressions on the 

 declivities of which they grew, lying with the top lowermost, always 

 having fallen towards the bottom of the valley, and showing indica- 

 tions that they have fallen from age and not from wind, and that they 

 are found in the order of superposition which has been stated. 



According to Vaupell, the earlier forests of Denmark were composed 

 of beeches, oaks, firs, aspens, willows, hazel, and maple, the first three 

 being the leading species ; but these have now been superseded by the 

 * Edinburgh : Oliver and Boyd, 1877. 



