40 Origin of the British Flora. 
channel across the low neck of land just beyond the 
southern limit of the ice-sheet. Other parts of Britain 
were hidden under ice-sheets whose gathering grounds had 
other centres, and the result seems to have been the total 
blotting out of the flora over the area north of the Thames 
and Severn, with the possible exception of certain high 
hills which rose above the ice. Even these were probably 
so smothered with snow that only the steeper crags were 
bare in summer. 
The condition of the greater part of Britain during the 
climax of the Glacial Epoch will not, therefore, greatly 
interest the botanist. The flora was so nearly extermin- 
ated that the interest is transferred to the non-glaciated 
strip between the Thames and Severn and the English 
Channel, and to a very small non-glaciated area in South 
Wales. In these parts only could the Arctic plants and 
mammals live, and the whole of Britain was so cold that 
the temperate species must have entirely disappeared. 
Many naturalists will disagree with the statement that 
has just been made ; for it has become almost an article of 
faith that there were certain warm corners in these Islands 
where the Temperate animals and plants could survive, and 
where the peculiar Lusitanian flora of Cornwall and of the 
West of Ireland lingered on till the renewed warmth 
enabled the plants again to spread. It will be necessary 
therefore briefly to summarise the evidence on which the 
opinion above expressed has been founded.* 
The temperature of the sea and of the air do not neces- 
sarily correspond in the same regions; we will, therefore, 
first discuss the evidence as to the lowest temperature of 
the seas round Britain. For this purpose the former 
southern limit of the formation of shore ice, or ‘ ice-foot,’ 
* See ‘The Climate of Europe during the Glacial Epoch,’ atural 
Scdence, Vol. 1., No. 6, pp. 427-433 (1892). 
