"POSTGLACIAL FORMATIONS" OF SCOTLAND 673 



as heretofore defined. I refer to our peat-mosses. Everyone is 

 familiar with the fact that in and underneath these the relics of 

 forest vegetation frequently occur. In many places throughout 

 Scotland — as well in high grounds as in low grounds — the peat- 

 mosses cover at least two ancient forest-beds. Typically the older 

 forest-bed occurs at the base of the peat, while the younger tier of 

 trees rests upon, and is covered by, a variable thickness of peat. In 

 some bogs only a foot or two may separate the forest-beds, while 

 elsewhere the intervening peat may attain a thickness of many yards. 

 So far back as 1866 I endeavored to show that the very general 

 occurrence of these phenomena was indicative of climatic changes.^ 

 The forest-beds, I maintained, were the products of relatively dry 

 or continental conditions, while the intervening and overlying sheets 

 of peat indicated colder and wetter conditions. I further pointed 

 out that at the present time all our peat-mosses are more or less 

 rapidly decaying, and being denuded by rain and wind — that, 

 although peat is now forming here and there under favorable 

 conditions, still that this is exceptional — the rate of growth being 

 generally much exceeded by the rate of decay and removal. From 

 this striking fact I inferred that the cHmate of Scotland has become 

 drier since the formation of the peat overlying our upper forest-bed. 

 The earher writers on the origin of the Scottish peat with its 

 buried trees did not recognize the influence of climatic changes in 

 the destruction of the old forests and their subsequent entombment 

 in peat. According to them, the formation of the peat-bogs was 

 due to the overthrow of the forests, chiefly by man's hand, but also 

 perhaps by natural causes, such as tempestuous wind. The whole- 

 sale downfall of the forests, it was believed, had obstructed the 

 natural drainage of the land, and thus induced marshy conditions 

 favorable to the growth of sphagnum and its allies. More recently 

 it has been suggested by some writers that in certain cases the 

 drainage may have been interrupted by the heaping-up of banks 

 of sand, clay, or other superficial accumulations, across broad val- 

 leys, whereby the forests over wide areas may have been destroyed 

 by stagnant water, and thus have given rise to the formation of bogs. 

 This is a somewhat far-fetched explanation. If it had any evidence 



I Transactions 0} the Royal Society of Edinburgh, Vol. XXIV (1866), p. 363. 



