Eleee: Glacial Survivals. 315 
of these several live in Britain, and appear to have survived the 
Ice Age. 
If this existence of Mollusca during the Ice Age on the 
driftless region be accepted, we have a probable explanation of 
the distribution of two of our most characteristic northern 
shells, viz., dcanthinula lamellata and Margaritana margaritifer. 
Existing in Britain in pre-glacial times these two species might 
have lingered on within the driftless area during the Glacial 
Period. After its close they would spread out to the surround- 
ing districts. In the case of A. lamellata, this extended across 
the North Sea (then probably a land area) to Sweden, Denmark, 
and North Germany; in the case of the Pearl Mussel, to 
Scandinavia and Northern Germany. 
During the Glacial Period, therefore, the Cleveland driftless 
region probably supported a fauna and flora, chiefly of an 
Arctic character, though several temperate forms may have 
also existed. After the ice sheets melted it formed a centre 
of distribution from which animals and plants radiated to the 
surrounding bare lands. 
What has been here stated concerning North East Yorkshire 
is applicable, with modifications according to conditions, to 
other driftless areas. In this respect the peculiar flora of 
Teesdale is worthy of attention in relation to the glaciation of 
that valley. Dr. A. R. Dwerryhouse, in his valuable essay 
on the Ice Age in Teesdale,* shows considerable non-glaciated 
regions. May not an Arctic fauna or flora have existed here 
during the Ice Age, including the rare northern plants for 
which the district is famous? A careful study of the flora and 
fauna (especially Coleopfera) in relation to these areas might 
reveal some interesting features. 
It seems probable that the biological study of unglaciated 
areas will decide the problem of glacial survivals, temperate or 
Arctic. That the whole of our pre-glacial fauna and flora was 
destroyed during the Ice Age seems improbable, and in con- 
sidering that of any ice-free country, discrimination must be made 
between the purely pre-glacial species (e.g., M/udzlla europea, the 
Heaths, A. lamellata, M. margaritifer) ; the Arctic species (e.g., 
Miscodera artica, Alpine Beetles, the Crowberry, Dwarf Cornel, 
etc.) ; and the species which have invaded the district since the 
Ice Age. At best, however, only probabilities and possibilities 
can be asserted, unless well-preserved fossils conteniporaneous 
with glacial beds be found in any particular district. 
* *Quart. Journ. Geol. Soc.,’ 1902. 
1907 September I, 
