CHAPTER XX 
THE ORIGIN OF OUR BRITISH FLORA 
Wuat is known of the European flora before the great 
series of Ice Ages had entirely altered its character is in 
a way satisfactory and yet a little bewildering. 
In Eocene, Miocene, and Pliocene times in France, a 
very strange mixture of plants have been recognised. In 
the same stratum there may occur two species which are 
now separated by, for instance, the entire width of Europe 
and Asia, or what is much more difficult to understand, 
two forms which we now consider characteristic of 
temperate and subtropical climates respectively, and yet 
which had, in the Ardéche, been involved in the same 
volcanic eruption and whose fossil leaves are found side 
by side. 
It is supposed that these French deposits show a 
distinct change of climate. In the Upper Pliocene they 
seem to suggest that the Great Ice Age is already looming 
in the distant future. But on the whole, M. Laurent 
refers to the fertile valleys of the Caucasus as explaining 
this mixture of different vegetations in the flora of 
Cordagne and Charay at that very ancient date. 
When the glaciers invaded Northern France and 
covered the whole of North-western Europe, from 
Norfolk upwards, in a winding sheet of snow, the 
ancient European flora was of course in large part 
destroyed. 
It seems that even before those days many species and 
perhaps the present kind of temperate deciduous wood- 
lands were to be found on the Pyrenees, Alps, and 
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