The Origin of our British Flora 



the oak had also succeeded in invading Scotland. But 

 this is just the point where the difficulties begin, for it 

 is known that when the ice began to vanish away 

 from our islands there was no regular steady improve- 

 ment of climate, but many fluctuations and changes 

 which are not yet understood. 



Even in Sweden it has been shown that the hazel 

 once occupied many districts from which it is now 

 absent. To-day it only occupies two-thirds of the 

 country which it had conquered during the time that 

 followed the first great shrinking of the glaciers. Gunnar 

 Andersson supposes that Sweden of to-day is distinctly 

 colder (about 2.4° C. less in mean annual temperature) 

 than in the flourishing period of the hazel.-^*^ These 

 changes of temperature belong to a very intricate series 

 of geological questions upon which the writer is not 

 competent to give an opinion. 



It is generally allowed by all continental botanists 

 that after the first and greatest of the Ice Ages, a long 

 period of time ensued during which the climate was 

 hotter and drier than it is to-day. Then followed a dis- 

 tinct relapse into a Little Ice Age, which was by no means 

 so severe as the Great one, but yet cold and wet enough 

 to leave very distinct traces.* This relapse is accurately 

 shown in Dr. Lewis's sections of peat-mosses. A layer 

 of arctic plants occurs between an upper and a lower 

 forest. So in the Merrick hills, at about 800 feet, a dis- 

 tinct layer of Empetrum is found. This plant does 

 not now grow in this district below at least 1500 feet. 

 The climate was therefore distinctly worse than it is 



* Mr. Lamplugh, in a polemical address to the British Association, denied 

 the existence of any of the climate changes worked out in detail by Professor 

 James Geikie. But even in this very paper he admits changes of some sort, 

 and every continental geologist seems to agree to one if not more warm inter- 

 glacial periods. 



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