CHAP. XV. IN THE PLAINS OF THE PO. 307 



down from Mont Cenis, and had travelled as far as Avi- 

 gliana ; also masses of serpentine, brought from less remote 

 points, some of them apparently exceeding in dimensions 

 the largest erratics of Switzerland. I afterwards visited, 

 in company with Signori Grastaldi and Michellotti, a still 

 grander display of the work of a colossal glacier of the olden 

 time, twenty miles NE. of Turin, the moraine of which 

 descended from the two highest of the Alps, Mont Blanc 

 and Monte Rosa, and after passing through the valley of 

 Aosta, issued from a narrow defile above Ivrea (see map, 

 fig. 43). From this vomitory, the old glacier poured into 

 the plains of the Po that wonderful accumulation of mud, 

 gravel, boulders, and large erratics, which extend for fifteen 

 miles from above Ivrea to below Caluso, and which, when 

 seen in profile from Turin, have the aspect of a chain of 

 hills. In many countries, indeed, they might rank as an im 

 portant range of hills, for where they join the mountains they 

 are more than 1,500 feet high, and retain more than half that 

 height for a great part of their course, rising very abruptly 

 from the plain, often with a slope of from 20 to 30. This 

 glacial drift reposes near the mountains on ancient meta- 

 morphic rocks, and farther from them on marine pliocene 

 strata. Portions of the ridges of till and stratified matter 

 have been cut up into mounds and hillocks by the action of 

 the river, the Dora Baltea, and there are numerous lakes, so 

 that the entire moraine much resembles, except in its greater 

 height and width, the line of glacial drift of Perthshire and 

 Forfarshire, before described, p. 248. Its complicated struc 

 ture can only be explained by supposing that the ancient 

 glacier advanced and retreated several times, and left large 

 lateral moraines, the more modern mounds within the limits 

 of the older ones, and masses of till thrown down upon the 

 re-arranged and stratified materials of the first set of moraines. 

 Such appearances accord well with the hypothesis of the 



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