3 1 6 PREHISTORIC E UROPE. 



Thus on both sides of the Alps we have evidence to show 

 that the Glacial Period was not a long uninterrupted period of 

 cold conditions, but that it was characterised by oscillations of 

 climate, comparable with those which marked the Ice Age of the 

 British Islands and Northern Europe. It is true that hitherto 

 we have discovered evidence in Switzerland and Italy of only 

 one interglacial epoch. We are not, however, justified in con- 

 cluding from this that only one such epoch interrupted the 

 Glacial Period — that the glaciers only twice invaded the low 

 grounds. The positions in which the Italian and Swiss lignites 

 have been preserved are wholly exceptional. The Val Borlezza 

 could only be converted into a lake by a glacier blocking its 

 mouth, and this happened twice. But there may have been 

 glacial epochs both earlier and later, when the glaciers did not 

 extend so far. Of such cold epochs and of the milder eras which 

 may have separated them, the Val Borlezza might well preserve 

 no recognisable trace. And the same may be said of the basin 

 of Leffe. A mountain region, as I have remarked above, is the 

 least likely in which to look for the relics of interglacial times. 

 The very places (viz. valley-bottoms) in which freshwater beds 

 would be deposited, are just those adown which the glaciers of 

 a succeeding cold epoch would advance, crushing, grinding, and 

 ploughing on their way. The conditions under which the 

 lignites of Leffe and the Yal Borlezza have been accumulated 

 were thus, as I have said, quite exceptional — they owe their 

 origin more or less directly to the former great extension of the 

 glaciers, but their preservation is due to the fact that the valleys 

 in which they occur were not ploughed out by glacial action. 1 



1 It is still an open question whether the great frontal moraines of the plains 

 of Piedmont, Lombardy, and Yenetia, mark the extreme limits reached by the 

 glaciers during the climax of the Ice Age. These moraines are underlaid by great 

 accumulations of coarse gravel and shingle, much of which no doubt was laid 

 down by rivers flowing from the glaciers at the time of their advance. But all 

 the shingle-beds, which are frequently hardened into conglomerate, cannot be 

 so accounted for. I refer especially to those wide-spread masses of conglomerate, 

 which are called Ceppo by the Italian geologists, and assigned by them to the 

 Pliocene Period. Through these deposits the glaciers have ploughed their way 

 in precisely the same manner as the glaciers of the latest glacial epoch in Swit- 



