486 PREHISTORIC EUROPE. 



dently grown upon the margin and steep inner slopes of the 

 basin. Above them succeed trunks of oak (Quercus sessiliflora), 

 which are likewise buried in peat, and have evidently fallen in 

 from the sides of the basin, in the same manner as the Scots firs. 

 The uppermost portion of the peat is marked by the presence 

 of the alder. Such is the general succession met with along 

 the margin or outer zone of the basin. In the central region 

 remains of trees are not so abundant. The bottom-portions are 

 composed exclusively of moss-peat. Farther up, however, roots 

 and trunks of stunted pines make their appearance, indicating 

 in some swamps as many as two or even three distinct layers of 

 roots and trunks of such pines. Still higher up the pine dis- 

 appears and is replaced by white birches, and afterwards by 

 alders and hazels. The pines and oaks of the outer woody zone 

 were noble trees, the former often attaining a thickness of three 

 feet, and being correspondingly tall. Many of the oaks are 

 even thicker, measuring often four feet in diameter. The close 

 juxtaposition of the stools and the straightness of the trunks 

 show that the forest -growth was dense. These facts teach us 

 that before the peat had commenced to accumulate Denmark 

 was bare and devoid of forests. Its surface was dappled with 

 lakelets and pools, and covered with a scanty arctic flora, the 

 character of which betokens a climate bike that of Lapland and the 

 far north. By and by, however, the climate became less severe, 

 and aspens and pines gradually overspread the land, the thick 

 bark of the latter betokening colder winters than Denmark now 

 experiences. The trees appear to have crowded everywhere, 

 growing densely along the margins of pools and lakelets, which 

 water-plants and mosses were converting into marshes. From 

 time to time, borne down by wind, or age, or snow, the trees fell 

 into the marshy basins, pools, and swamps, and were there by 

 degrees buried in the accumulating peaty matter. A gradual 

 change of climate is evinced by the drying -up of many of the 

 basins, and the appearance of pines which flourished upon the 

 surface of the bogs themselves, and the change is still more 

 strongly indicated by the advent of the oak, which eventually 



