374 Relation of the Plant Population to the Glacial Period. 
of our southern flora, which occurs in a similar way stranded in 
some of the warmest low-lying parts of Britain. 
The discussion is limited to the Relation of the Present 
Plant Population of the British Isles to the Glacial Period. 
Our problem is a special one ; it is not the same as that which 
confronts the botanist on the Contineent of Europe or America ; 
and it is not the problem of the origin of the flora of an oceanic 
island. Also, the wider question of the origin of the species 
composing the British flora is outside the discussion, for it 
would lead us into too many untrodden bypaths, and could not 
satisfactorily be gone into in the present imperfect state of our 
knowledge. 
Perhaps it will be well to explain at once why the inquiry 
is thus limited to comparatively recent periods, and how it is 
that we need not explore the unknown earlier periods and deal 
with larger questions. 
Our first inquiry in this case must be: Has there been any 
continuous occupation of Britain by a temperate flora and 
fauna from pre-Glacial times to the present day? Or, to put 
it in other words: Are any of our plants survivors that 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 I think that all geolo- 
gists 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. 
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. 
The glaciation in Ireland was even more extreme, for 
apparently no part of Ireland escaped. Even the warmest 
Naturalist, 
