The Origin of our British Flora 
Geikie’s arrangement of the various Ice Ages. These are 
as follows for Scotland :— 
Most recent Upper Peat-bog or 6th Ice Stage. 
Glaciers in Highland corries. Snowline at 3500 feet. 
Peat above Upper Forest: raised beaches at 25 to 30 feet. 
Somewhat cold and wet climate. 
Upper Forest or 5th Interglacial Stage. 
Upper Forest. Climate relatively dry and genial. 
Land area somewhat greater than to-day. 
Lower Peat-bog or 5th Glacial Stage. 
Glaciers in Scottish valleys. Average snowline 2400 to 
2500 feet. Raised beaches at 45 to 50 feet. 
Cold and wet climate. Lower peat deposit. 
Lower Forest or 4th Interglacial Stage. 
Genial climate with a greater land area than exists to-day. 
Lower forests or morainic accumulations of 4th Ice Age. 
Oldest or 4th Ice Age (Mecklenburgian). 
Large glaciers in Scottish Upland and Highland valleys. 
District Ice sheets. Raised beaches at 100 to 135 feet. 
Arctic climate with the permanent snow at 1000 feet in 
west and north-west, to 1500 or thereabouts in central 
Scotland. 
But there is a difficulty with regard to the latest of 
these deposits. Above the lower forest there is from 4 
to 9 feet of peat, chiefly composed of sphagnum moss. 
How many years are required to form this thickness of 
peat? Unfortunately the rate at which peat accumulates 
is so variable that no definite answer can be given to 
this question, but nine hundred years would surely be 
enough for this accumulation, which would bring us to 
about 1000 A.D. 
Now in Scotland there is strong evidence for the ex- 
istence of great forests which existed, at any rate, at that 
date, and continued over much of the country until at 
least the period of the Border wars, The great oak 
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