256 James Geikie — On Changes of Climate. 



Diiniten could not be due to mere local causes affecting Switzerland 

 alone — they must have left their mark over a wide area in Europe. 

 It is therefore not unreasonable to expect that among the glacial 

 deposits of Italy we ought to find some traces of former oscillations 

 of climate. As far as I am aware, however, no such traces have yet 

 been recognized. All that has been asserted in regard to the old 

 Italian glaciers is simply this — that they once deployed upon the 

 plains of Piedmont, and finally retired, leaving behind them, as 

 marks of their ancient extent, the gigantic moraines of the Dora 

 Baltea, the Dora Eiparia, and those in the neighbourhood of Arena. 



It will be remembered that one of the strongest objections to Prof. 

 Eamsay's theory of the origin of lake-basins by glacial erosion, was 

 the fact that the vast glaciers of Italy had actually crept ujDon the 

 plains of Piedmont, without excavating any great cavity in the soft 

 Pliocene sands. ^ I have always felt that this objection would have 

 some force, if it could be shown that the so-called •' Pliocene " beds 

 which underlie the great 'moraines are really of preglacial age. 

 But this is just the point which has not yet been proved. The 

 mammalian remains in the old alluvium certainly do not prove it, 

 neither do the shells which occur in the underlying marine sands. 

 Of the nine species of moUusca mentioned by Martins and Gastaldi 

 as characteristic, seven are still living in the adjoining seas, one is 

 doubtful, and only one is said to be extinct. There is nothing, 

 therefore, in the fossil-evidence to show that these beds are of pre- 

 glacial age : as far as that goes, they might quite well belong to 

 interglacial or still more recent times. 



If interglacial beds do not now occur in the north of Italy, it is not 

 because they never existed ; their absence can only be accounted for 

 by denudation. During that long interglacial period in Switzerland, 

 when the colossal glaciers had shrunk back to the deep Alpine 

 valleys, and oaks and pines clustered along the borders of the Swiss 

 lakes, the vast glaciers of the Italian Alps must likewise have retired, 

 and vegetation must then have followed their retreating steps to- 

 wards the mountain fastnesses. When the cold returned, and the 

 glaciers of Switzerland once more ploughed their way outwards, 

 until they reached a point far beyond where the lignite-beds are 

 now found, it is equally certain that this ice would creep down the 

 Italian valleys, and might well deploy upon the plains of Piedmont, 

 here scooping out, and there covering up with debris the aqueous 

 deposits which had gathered in its absence. All that the last great 

 advance of the glaciers could do would be to deepen rock-basins 

 which had been hollowed out in the preceding cold periods of the 

 glacial epoch, and slightly to erode and smooth valleys whose 

 origin dates back to times incalculably more remote than even the 

 dawn of the glacial epoch. If during the last interglacial jDcriod, 

 when the Diirnten beds were being formed, all the great lake-basins 

 of the Alps had been silted up, it is highly improbable that these 

 hollows would have been again cleared out by the last extension of 

 the glaciers. To have allowed such a silting-up by streams and 

 ^ Antiquity of Man, p. 313. 



