igii- Rrid. — Briiish P/anfs and the Glacial Pe7iod. 203 



managed to live through the cold of the Glacial period in 

 some warm nook in Britain ? They evidently found a refuge 

 somewhere, for we know that the same temperate species 

 that live in Britain now were here in pre-Glacial times. But 

 was this refuge in Britain ? 



Here geology comes to our aid, and 1 think that all 

 geologists who have made a special study of the climatic 

 conditions will agree with me. Any survival of our flowering 

 plants, except in the case of a few arctic and alpine species, 

 was quite impossible. 



It may come as a shock to some of my colleagues when I 

 say that for this particular discussion we have a perfectly 

 definite starting-point. We have merely to account for the 

 incoming of our existing flora, after an earlier assemblage had 

 been swept away almost as completely and effectually as 

 the celebrated volcanic eruption wiped out the plants of 

 Krakatoa. 



In order to make clear the existence of this limitation, 

 and for the convenience of the discussion, I have prepared 

 certain maps, which are now shown. I propose now to say 

 a few words as to the bygone climatic and orographic 

 changes indicated on those maps, and on their bearing on 

 the existing flora of Britain. I must say at once, however, 

 that you must not take these maps as absolutely exact 

 statements as to the climatic and geographic conditions at 

 the different stages involved in our inquiry. But they give 

 the result of many years' work at this subject, and, I think, 

 may be accepted as embodying the main factors which 

 dominate the question we have to discuss. 



We know that during the greatest intensity of the cold all 

 Scotland, Ireland, and the greater part of England were 

 buried under ice and snow — except, possibly, for some high 

 peaks on which a few arctic species survived. Ice filled the 

 North Sea and covered the lowlands of England down to 

 the mouth of the Thames. Without crossing the Thames 

 it almost reached London. Its southern limit stretched to 

 South Wales, where tongues of ice reached the Bristol 

 Channel in big glaciers like those of the Antarctic Regions or 

 Greenland. In South Wales a few hills may have escaped, 

 though surrounded by ice. 



A 2 



