

GEOLOGICAL SURVEYING 319 
these ancient lakes date back to the glacial period. Even 
those lacustrine deposits which are entirely of post-glacial age, 
have often yielded interesting fossilk—amongst which may be 
mentioned remains of the ancient types of oxen (Bos primz- 
genius, B. longifrons), the great Irish deer, wolf, beaver, etc., 
not to mention relics of prehistoric man. Freshwater shells 
also frequently occur, forming beds of shell-marl. 
Very few broad river-valleys fail to show old terraces of 
gravel, sand, etc., occurring at various levels above the present 
streams. These mark levels at which the rivers formerly 
flowed. Terraces of this kind are best developed in valleys 
which have been more or less abundantly clothed with glacial 
and fluvio-glacial deposits: or in regions where the rocks have 
yielded not less readily to fluviatile erosion. In a country 
like Scotland, where the rocks are all relatively “hard,” old 
river-terraces may be said never to occur outside of preglacial 
valleys. So long as our rivers follow their preglacial 
courses, those terraces are almost invariably in evidence—the 
rivers making their way through broad open valleys. No 
sooner, however, does a stream leave its preglacial course to 
cut its way through the older rocks, than the whole character 
of the valley changes. The stream no longer flows through 
a wide terrace-fringed valley, but through a relatively narrow 
ravine. 
PEAT.—-Reference has been made to the occurrence of 
peat in old lacustrine depressions. But, as everyone knows, 
peat often covers wide areas of rolling low ground and high 
plateau, and even swathes relatively steep mountain slopes. 
In some regions, indeed, it is found capping flat hill-tops. 
There is no difficulty in mapping peat-bogs, but a careful 
study of their phenomena has still to be made. It is well 
known that many peat-bogs cover and conceal the stumps 
and stools of trees which are rooted in an ancient soil, and 
obviously, therefore, grew zz sztu (see Plate LIV. 2). Not 
only so, but deep cuttings in certain peat-bogs have revealed 
the presence of one or more such old “ forest-beds” occurring 
one above another in the peat itself. Scandinavian, Danish, 
and German observers have detected in the peat-bogs of 
Northern Europe similar phenomena, and have gathered 
much additional botanical evidence of varying climatic 


