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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