GLACIER ACTION. 261 



belonging to the plains and produced by erosion are connected 

 with the depressions in the Alps. 



After the hills and valleys were formed, the lowlands of 

 Switzerland were strewed over with pebbles. This work was 

 performed by the glaciers, as has been already shown in detail 

 (pp. 177, 178). When the glaciers descended from the region 

 of the Alps into the low grounds at the commencement of the 

 drift-period, they first filled up the valleys and lake-basins. Thus 

 they formed a bridge, over which the masses of stone which they 

 brought from the mountains could be carried forward to great 

 distances. If the lake-basins had not been covered by glaciers, 

 the masses of rubbish must undoubtedly have filled them up, 

 and we should therefore now find them, not in the neighbourhood 

 of the lakes, but in their beds. When the glaciers afterwards 

 retired, the waters of the lakes again became limpid. Obliga- 

 tion is therefore due to the glaciers for the preservation of the 

 lakes, which are among the chief ornaments of Switzerland *. 

 In those mountain-regions which are not covered by glaciers, 

 lakes are consequently wanting, as in the Himalayas, because, as 

 Falconer has shown, no glaciers have protected the clefts of the 

 mountains from being filled up with rubbish. 



Moraines have here and there been left by Swiss glaciers at 

 the outlets of lakes, so as to impede the outflow of water, and to 

 cause an elevation of the surface of the lakes. Thus, near Zu- 



* Professor Escher de la Linth has demonstrated this fact in his memoir 

 ' Ueber die Gegend von Zurich in der letzten Periode der Vorwelt,' 1852. 

 The occurrence of stratified drift under erratic blocks has led M. G. de Mor- 

 tillet to the opinion that the lake-basins were filled up with rubbish, but 

 afterwards hollowed out by the glaciers (see his l Carte des anciens Glaciers 

 du versant Italien des Alps/ and Gastaldi and Mortillet ' Sur la Theorie de 

 1'Affouillement Glaciaire '), so that the present lake-basins were produced by 

 the glaciers deepening and eroding their beds. Professors Ramsay and Tyndall 

 have gone still further, and suppose even the valleys of the Alps to have been 

 furrowed out by glaciers. These hypotheses are contradicted by the fact 

 that a glacier does not attack the ground beneath it very deeply (see p. 189), 

 as is shown by the termination of the Rosenlaui glacier, where the water 

 flowing off has hollowed out a deeper bed than the glacier above it. And 

 what powerful action must we assume for glaciers, as the depth of the Lago 

 Maggiore is 400 metres (or 437 yards), and the depth of the Lake of Como 

 is 409 metres (or 447 yards) ! Professors Studer and Desor have, with great 

 justice, stated their opinion against any such view of the case. 



