140 PROFESSOR JAMES GEIKIE ON THE 



them comes the well-known peat-bed (4). This is a mass of vegetable matter, varying 

 in thickness from a few inches up to 3 or 4 feet. In some places it seems to be made 

 up chiefly of reed-like plants and sedges and occasional mosses, commingled with which 

 are abundant fragments of birch, alder, willow, hazel, and pine. In other places it 

 contains trunks and stools of oak and hazel, with hazel-nuts — the trees being rooted in 

 the subjacent deposits. It is generally highly compressed and readily splits into laminae, 

 upon the surface of which many small reeds, and now and again wing-cases of beetles, 

 may be detected. A large proportion of the woody debris — twigs, branches, and trunks 

 — appears to have been drifted. A " dug-out " canoe of pine was found, along with 

 trunks of the same tree, in the peat at Perth. The Carse-deposits (5), consisting 

 principally of clay and silt, rest upon the peat-bed. The occurrence in these deposits of 

 Scrobicularia piperata and oyster-shells leaves us in no doubt as to their marine origin. 

 They vary in thickness from 10 up to fully 40 feet.* 



A similar succession of deposits is met with in the valley of the Forth, t and we can- 

 not doubt that these tell precisely the same tale. I have elsewhere | adduced evidence 

 to show that the peat-bed, with drifted vegetable debris, which underlies the Carse 

 accumulations of the Forth and Tay is on the same horizon as the " lower buried forest " 

 of our oldest peat-bogs, and the similar bogs that occur in Norway, Sweden, Denmark, 

 Schleswig-Holstein, Holland, &c. Underneath the " lower buried forest " of those regions 

 occur now and again freshwater clays, charged with the relics of an Arctic-alpine flora ; 

 and quite recently similar plant-remains have been detected in old alluvia at Corstorphine, 

 near Edinburgh. When the beds below our older peat-bogs are more carefully examined, 

 traces of that old Arctic flora will doubtless be met with in many other parts of these 

 islands. It was this flora that clothed North- Western Europe during the decay of the 

 last local ice-sheets of Britain and the disappearance of the great Baltic glacier. 



The dissolution of the large valley- glaciers of this country was accompanied by a 

 general retreat of the sea — all the evidence leading to the conviction that our islands 

 eventually became united to the Continent. The climatic conditions, as evidenced by 

 the flora of the " lower buried forest," were decidedly temperate — probably even more 

 genial than they are now, for the forests attained at that time a much greater horizontal 

 and vertical range. This epoch of mild climate and continental connection was even- 

 tually succeeded by one of submergence, accompanied by colder conditions. Britain was 

 again insulated — the sea-level in Scotland reaching a height of 45-50 feet above present 

 high-water. To this epoch pertain the Carse-clays of the Forth and Tay. A few erratics 

 occur in these deposits, probably betokening the action of floating ice, but the beds more 

 closely resemble the modern alluvial silts of our estuaries than the tenacious clays of the 

 100-feet terrace. When the Carse-clays are followed inland, however, they pass into 

 coarse river-gravel and shingle, forming a well-marked high-level alluvial terrace, of much 



* For a particular account of the Tay-valley Succession, see Prehistoric Europe, p. 385. 



+ Proc. Roy. Soc. Edin., 1883-84, p. 745 ; Mem. Geol. Survey, Scotland, Explanation of Sheet 31. 



\ Prehistoric Europe, chaps, xvi., xvii. 



