XCiV FLORA ORCADENSIS. 
peat beds between them marked the occurrence of 
colder and wetter climates. Each Forest Bed is the 
evidence also of a time when Britain had a wider 
extent than it has now, and we need no further proof 
of this than the buried forests that now are covered 
by the sea. He also traced the relation between 
these beds and the raised beaches. There is good 
evidence to show that the hundred-foot beach belongs 
to an epoch of cold conditions, for the shells that 
occur in the clay deposits of this beach are of Arctic 
facies. The fifty-foot beach also marks a time when 
the climate was less genial than it is now, as in 
the west of Scotland there were glaciers descending 
through the mountain valleys to sea-level at the time 
when that beach was being formed. But the fifty- 
foot beach rests on a buried Forest Bed in some parts 
of the estuaries of the Tay and Forth. This is 
probably the lower of the two Forest Beds that 
occur in the peat-mosses. Similarly, there are traces 
of an upper Forest Bed below the deposits of the 
twenty-five-foot beach. During the Forestian epochs 
the sea must have retreated to a considerable distance 
from our shores, and Orkney may have been joined to 
the mainland of Scotland, while Britain may have 
been united to Ireland and to the continent of 
Europe. In the intervening cold epochs, when the 
peat flourished greatly and the forests died out or 
retreated to the south—the “ Turbarian” periods— 
the land sank to 100 feet and to 50 feet below its 
present level, and the raised beaches were formed. 
Simultaneously there was an increasing accumulation 
of snow and ice in the higher grounds of Scotland, 
