420 PREHISTORIC EUROPE. 



date back to the period of local glaciers and swollen muddy 

 rivers which carried down to our estuaries the mud and silt of 

 the 45-50-feet level. When the sea had retired to its present 

 limits the climate had again become favourable to the growth 

 of forests, and trees grew over the surface of the C arse-lands, and 

 doubtless re-occupied much of the ground from which they had 

 been compelled to retreat during the ungenial period of local 

 glaciation and extreme humidity. In this manner new genera- 

 tions of trees would occasionally grow over the peaty surface, 

 beneath which the forests of early postglacial times lay buried. 



Although peat is commonly dug for fuel in many places 

 in Scotland, yet this is by no means so general as in Ireland, 

 Scandinavia, Denmark, Holland, Northern Germany, and other 

 regions, where coal is less easily and economically obtained. 

 The structure of the Scottish peat-mosses, therefore, is as a rule 

 not so well known as that of the turbaries of other countries. 

 The general phenomena, however, are sufficiently familiar. 

 Peat occurs in Scotland covering here and there wide areas in 

 the Lowlands, and still more extensive regions in the Southern 

 Uplands and the Highlands. It varies in thickness from a foot 

 or two up to ten yards and even more. On hill-tops and hill- 

 slopes it is rarely deeper than from three to six feet, the 

 thickest accumulations occurring upon undulating low grounds 

 and table -lands, and in the bottoms of mountain -valleys. 

 Almost everywhere it covers over the remains of an old forest- 

 vegetation, amongst which the commoner trees are pine, oak, 

 and birch. Besides these, however, we find alder, willow, ash, 

 hazel, and juniper. These trees are often remarkable on account 

 of their 'great size and their wide distribution. Thus we find 

 roots and trunks of oak in the peat of Banffshire at a height of 

 3000 feet above the sea, although that tree now finds its 

 northern limits in Eoss- shire, Aberdeenshire, and Western 

 Inverness-shire, 1 and does not grow naturally in these northern 

 regions at nearly so extreme an elevation. The large size attained 

 by the bog-oaks has often been remarked upon. Thus in a peat- 



1 Cyhele Britannica, vol. ii. p. 409. 



