ICE AGES — SIMPSON 293 



This conclusion is becoming more and more accepted by glaciologists 

 as they work out the sequence of the glacial epochs in their own 

 regions, and a meteorologist cannot accept any other conclusion. In 

 the sequel, therefore, we shall consider that the glacial history of the 

 Alps is representative of the glacial history of the world as a whole. 



The advance and retreat of the ice must have been accompanied by 

 large variations in the climate. When a country such as Great 

 Britain was invaded by an ice sheet, the climate must have been that 

 of the polar regions today, and the fossils of plants and animals leave 

 no doubt that such was the case. The climate during the interglacial 

 periods, however, is much more interesting and unexpected. One 

 would not have been surprised if the climate during the temporary 

 retreat of the ice had remained cold and unpleasant. The evidence 

 however, is quite clear that in some, if not all, the interglacial epochs, 

 the climate became warmer and more genial than today. At Hotting, 

 in the Alps near Innsbruck, fossil leaves have been found of a rho- 

 dodendron which grows today only in Portugal and the Caucasus, 

 where the temperature is higher and the rainfall greater than it now 

 is in Hotting; in the rivers of Europe (including the Thames) the 



12 Elnhelten s t 



(L II 1 



Cheile'en > <Moustdrlen > 



MB 



Jahrtausende 20 7 

 Figuee 2.— Penck and Bruckner's diagram of height of snow line in Alps during the Pleistocene ice age. 



shells of fresh-water mollusks are found which now survive only in 

 rivers such as the Nile, the temperature of which is 10° C. higher 

 than that of the European rivers of today; and on the coasts of 

 Holland and Denmark, beds of sea shells were deposited containing 

 species 18 percent of which today only occur south of the Bay of 

 Biscay. 



There is still considerable controversy as to which of the interglacial 

 epochs these finds should be referred ; so that we do not know whether 

 all the interglacial epochs had warmer and wetter conditions than are 

 experienced today. But there can be no doubt that in one or more 

 of the interglacial epochs the climate not only returned to present-day 

 conditions but also became warmer and wetter. 



Outside the areas which were invaded by the ice — the so-called 

 glaciated regions — we must look to other records than those of ice to 

 give us information regarding the changes of climate which occurred 



