262 NATURAL SCIENCE. Oct., 



the continued existence of temperate life and also to enlarge our 

 conception of the area free from ice. 



There are other considerations which strengthen this view. The 

 southern limit of the ice, when found, marks its extreme winter 

 extension ; during summer a very much larger area of country would be 

 free from ice ; for it is to be remembered that, whatever theory of 

 glaciation we accept — since those involving an absolute diminution of 

 solar heat are almost universally discarded — we have to reckon with 

 a summer heat-supply as great as that which we receive to-day. 

 Consider, then, what would be the effect of setting our present summer 

 to work on an England in which the ice reached as far south as 

 London. We may surely assume the melting back of the ice for a 

 considerable distance. 



During the most intense Glacial period possible, according to 

 the astronomical theory, our present heat-supply was concentrated 

 into 1 66 days, but this would probably affect very little its melting 

 powers ; and according to Sir Robert Ball's data, the average 

 temperature of the Glacial summer would be 42 F. higher than at 

 present, or about 102° F. Such a considerable retreat of the ice 

 during summer would, of course, tend to make temperate life more 

 possible in the country. 



Again, there is evidence which appears to show that the Gulf 

 Stream warmed our western and southern shores as it does to-day. 



(1) It has been noted that more southern forms of shells occur in 

 the Drift of the west of England and of Ireland than in that of the 

 east of England. 



(2) Glaciation extended further south in North America than in 

 Western Europe. 



Therefore, as at the present day there are places considerably 

 north of London with milder climates, so during glaciation there may 

 have been areas fitted to preserve temperate forms of life besides the 

 southern counties before mentioned. 



But do the fossils of our Glacial deposits favour the view of the 

 survival of any pre-Glacial plants and animals in our country ? 



Intercalated with the Boulder Clay are certain sands and gravels 

 containing occasionally organic remains, which those who accept the 

 view of interglacial warm periods claim as evidence of such. 



If, as I have endeavoured to show, 1 the evidence for such periods 

 is inconclusive, these organic remains may indicate survival ; and it 

 is well-known that such mingling of arctic and southern forms does 

 not necessarily indicate alternations of warm and cold periods. 

 Professor Forbes pointed out an interesting example in his " Fauna 

 and Flora of the British Islands." Cape Cod, in North America, 

 he remarked, forms the line of demarcation between a fauna as 

 northern as that of England during the Glacial period, and another of 

 an aspect perhaps even more southern than that existing at present 

 1 Geological Magazine, August and September, 1891. 



