PHYSICAL CONDITIONS— POSTGLACIAL. 529 



mena in the peat-bogs of Scania. There, as in Norway, the 

 bottom forest-beds are composed of leafy trees, while the upper 

 ones are principally coniferous. I have searched through many 

 papers and books descriptive of the peat -bogs of Holland, 

 Schleswig-Holstein, and Northern Germany, but cannot find 

 that the same succession is as well marked in those regions. 

 Very often, indeed, no discrimination is made between the trees 

 which have come from the lower and upper parts of the peat, 

 the writers simply stating what kind of trees are met with. I 

 cannot doubt, however, that if the succession had been as con- 

 spicuous as it is in Norway and Sweden, so remarkable a cir- 

 cumstance would not have been overlooked. 



How are we to explain these phenomena ? It is obvious that 

 they are too general to be accounted for by merely local causes. 

 If the bottom peat-beds be due to a formerly prevalent cold and 

 wet climate, we can hardly escape from the conclusion that the 

 upper layer of peat points to a recurrence after some interval of 

 similar conditions. The presence of the upper forest-layer 

 shows that the wet period came at last to a close, and was suc- 

 ceeded by a drier climate favourable to the growth of trees. 

 And from the fact that in many parts of Scotland, Ireland, and 

 Scandinavia, the forests which then overspread the land were 

 composed in large measure of pine and birch, we may reason- 

 ably infer that the climate was not so mild as during the growth 

 of the more ancient forests, the remains of which occur at the 

 bottom of the bogs. 



The subsequent destruction of these later forests and their 

 burial in sphagnum-peat indicate a relapse to ungenial and wet 

 conditions. And it is suggestive that this change was followed 

 or accompanied by a rise of sea-level and the submergence of 

 forest-covered tracts in many maritime regions. Most of the so- 

 called submarine forests which appear upon the low shores of 

 our own and neighbouring lands belong to the second forest 

 period, although not unfrequently both upper and lower forest- 

 beds are exposed upon the same beaches. The whole subject 

 of these successive forest-beds, with their intervening layers of 



2 M 



