408 Br. Du Riche F Teller — The Moraine Walls 



plain. 1 The extreme limit of the maximum glaciation, as indicated 

 by the outermost moraine walls 10 to 12 kilometres south of the 

 lower ends of the Lakes Orta, Maggiore, Como, and Garda, is shown 

 in Sheet No. 2, Figs. II, III, and IV. 



II. The Glaciers and the Sea. in the Po Valley. 

 The maximum glaciation south of the Alps presents a striking 

 contrast to that on the north in that it was marked by a uniform 

 general advance of more or less self-contained glaciers of the fan or 

 Piemont type, which invaded the Po Valley to a distance of 10 to 12, . 

 in the case of the Dora Baltea (Ivrea) glacier even 20 kilometres, 

 while north of the Alps the glaciers spread all over the Swiss 

 lowlands and deposited their terminal moraines even beyond. Thus 

 the maximum length of the southern glaciers, measured from the 

 crest-line of the Alps to their terminal moraine walls, does not exceed 

 100 kilometres, while on the north the Phone and the Rhine glaciers, 

 extending beyond the Jura and Lake Constance respectively, reached 

 a length of 300 kilometres, or three times as much. Inversely, the 

 quantity of material carried and deposited by the southern glaciers 

 having an average fall of 1 in 100, was immensely greater than that 

 of the northern glaciers, the average fall of which was only about 

 half the above. Hence the enormous accumulations of glacial 

 material in Piemont and Lombardy, where, moreover, the glaciers on 

 emerging from the valleys were arrested by the sea as an effectual 

 barrier to their further advance into the Po Valley. This Upper 

 Pliocene sea, an arm of the Adriatic, must have lasted well into the 

 Pleistocene period, and the glaciers washed by it must have been 

 stationery for a very long lapse of time, as is shown by the double 

 and triple concentric frontal moraine walls, each of which marks 

 a long halt in the slow retreat of the ice. 2 No less certain is it that 

 the sea must have been at a level much higher than the present 

 Po Valley, and higher even than the present levels of the lakes, for 

 the Pontegana marine shell-bearing deposit in the Breggia Valley 

 north of Como is at 300 metres altitude, which is 87 metres above 

 Lake Como, 197 metres above Milan, and 240 metres above the Po at 

 Piacenza, while the Fino deposits south of Como are at an altitude of 

 even 370 metres. It is therefore obvious that at the advent of the 

 maximum glaciation, arms of the SQa reached as far as the fjords 

 which constitute the present lake basins — a phenomenon which has 

 an important bearing on the age and origin of the lakes themselves. 



1 The principal localities of interglacial deposits between Lakes Maggiore, 

 Lugano, and Garda, and beyond are the following : at Be, in the Vigezzo 

 Valley, east of Domo d'Ossola ; at Calprino, near Lugano ; at Leffe and 

 Gandino in the Seriana Valley, north of Bergamo ; at Pianico in the Oglio 

 (Lake Isco) Valley ; at Valmarino in the Piave Valley, north of Treviso ; in 

 the Tagliamento Valley, north of Udine ; and in the Isonzo Valley, north of 

 Gorizia. 



2 It is a striking feature that, of the moraine walls, those of the Como 

 district are continuous, because the Adda eroded its bed marginally from the 

 Lecco arm of the lake, whereas the rivers of Ivrea, Lake Maggiore, and Lake 

 Garda (Dora Baltea, Ticino, and Mincio) found their exit more through the 

 centre of the frontal moraines, which are therefore broken up into agglomerations 

 of hillocks. 



