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 ^th hiterglacial Stage. 



Upper Forest. Climate relatively dry and genial. 

 Land area somewhat greater than to-day. 

 Loiver Peat-bog or ^th 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 /^th Ice Age (Meckle?iburgiati). 



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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