James Geikie — On Changes of Climate. 257 



rivers, however, the latest interglacial period must have been very 

 prolonged indeed ; of much greater duration, in fact, than we have 

 any grounds for believing it to have been. But what could not be 

 effected by streams and rivers, might yet be accomplished by the sea. 

 If while the last interglacial period endured, and the elephant and 

 its congeners wandered along the shores of Zurich and the Lake of 

 Constance, the north of Italy happened to be submerged to a depth 

 of 800 feet or thereby below its present level, then it is conceivable 

 that some of the great rock-basins at the mouths of the Alpine 

 valleys might become filled up with marine deposits. Now this 

 is just what I would infer did take place in the early stages of 

 the last interglacial period, and the so-called " Pliocene sands " are 

 the deposits which I am inclined to believe were then laid down. 

 While the genial climate which marked the deposition of these 

 sands continued to prevail, it would seem that the movement of 

 subsidence which had brought the base of the Alps within reach 

 of the waves was reversed, and the land once more appeared. 

 Elvers then flowed over what had recently formed the bed of 

 the sea, and deposited those alluvia in which the remains of Masto- 

 don, Hippopotamus, etc., are entombed. As this mild period drew 

 to a close, snow and ice again thickened in the valleys, and 

 torrents in summer-time overspread the plains of Piedmont with 

 great deposits of gravel — the Alpine diluvium of Italian geolo- 

 gists. When the glaciers once more issued from their deep valleys, 

 they would be unable to clear away the immense deposits of 

 diluvium and marine sand which had collected during the previous 

 mild interglacial period. And thus it seems to me not improbable 

 that large and deep rock-basins do really exist below the marine 

 sands of Piedmont at those points where the valleys of the Dora 

 Baltea and the Dora Eiparia open upon the great plains. 



In support of this opinion, it may be remarked that along the 

 frontiers of the Alps, between Arena and Rivoli, there appears to be 

 an entire absence of the grundmorane, which in Switzerland extends 

 to such a distance beyond the limits reached by the newer moraines 

 that overlie the lignites.^ It is hardly conceivable that, during the 

 accumulation of the Swiss grundmorane, the glaciers of Italy never 

 extended further south than the ground now occupied by the great 

 moraines. Mere difference of latitude does not enable us to get over 

 this difficulty. We may readily admit that the Italian glaciers would 

 be arrested in their downward course sooner than those of Switzer- 

 land ; yet the vast extent of the Swiss grundmorane indicates a 

 former intensity of cold, which must needs have given rise to glaciers 

 in Italy of even greater magnitude than those which piled up the 

 gigantic moraines of Ivrea. If, however, it be possible to admit the 

 interglacial age of the marine sands, etc., of Piedmont, then all our 

 difficulties vanish, and the absence of lake-basins and older glacial 

 deposits is at once accounted for.^ 



^ Unless, indeed, some of those large erratics which are found upon the hills above 

 Turin be the representatives of the older Swiss moraines. Gastaldi, however, believes 

 them to be of Miocene age. 



2 When, some time ago, I communicated to my friend, Prof. Ramsay, a rough out- 

 VOL. IX. — NO. xcvi. 17 



