OF LAKE-BASINS. 659 



ice up such an incline ? Before admitting this, it would be desirable, 

 in this case also, to see the practicability of the result established by 

 mathematical calculation on mechanical principles. 



Further, one of the greatest of the ancient Piedmontese glaciers, 

 fed by the snows of Mont Blanc and Monte Rosa, descended the Val 

 d'Aosta, to stretch far into the plain, and leave the enormous moraine of 

 Ivrea, close upon the Po. The course of this glacier is marked by no 

 great lake-basin, like those of lakes Maggiore and Como. If the latter 

 were eroded by glaciers, how is the absence of a lake-basin in the case 

 of the former to be explained ? The same argument will apply to the 

 important moraine of Rivoli near Turin, and to the smaller moraines 

 between the Stura and the Dora Eiparia, the whole of which are 

 unaccompanied by rock-basin lakes. Superficial moraine-tarns are 

 beside the question. 



The expressions used by me did not differ materially from those 

 employed by that eminent philosopher Sir John Herschel : — ' In the 

 upheaval of any extensive tract of land from the sea, hollows fitted for 

 lake-basins cannot fail to be left. If the upheaval be rude and pa- 

 roxysmal, resulting in the formation of mountain-chains, and accom- 

 panied with fracture and dislocation of the strata, such hollows will be 

 deep, precipitous, and narrow, in proportion to their length. Such is 

 the general character of lakes in mountainous regions — of the Swiss 

 lakes for instance, of those of North Italy, &c.' (Physical Geography, 

 1 Encyc. Brit.' vol. xvii. p. P91). Mortillet also, who maintains the 

 questionable hypothesis that the lake-basins were first filled up by silt 

 and then scoured out by the descent of the glaciers, expresses himself 

 thus, in reference to the Italian lakes : — 



' Le dernier soulevement des Alpes, qui a eu une puissance enorme, 

 a dii produire dans les fonds des vallees de grandes inegalites de sol, de 

 nombreux bassins ; en effet nous voyons ces vallees etre une succession 

 plus ou moins frequente d'etranglements et d'elargissements,' &c. 

 ('Anciens Glaciers Ital.' p. 17.) 



My object on the occasion referred to was to endeavour to account 

 for the remarkable difference between the Himalayahs and the Alps in 

 the important physical feature of lake-basins, which are absent in the 

 transverse valleys on the southern sides of the former, while they abound 

 in the latter. With the exception of greater and lesser elevation, and 

 magnitude of development, the two chains repeat each other in all their 

 primary orographic conditions. It seemed clear that the difference 

 must depend upon some secondary attribute, which might or might not 

 be present in a mountain chain. The enormous frontal moraines which 

 bound all the Italian lakes to the south made it certain that their 

 basins had been in the track of glaciers of vast magnitude, and which 

 had existed during long protracted periods. Conversely, lake-basins 

 were wanting in corresponding situations in the Indian mountains, and 

 glaciers, according to every aspect of the evidence, had never descended 

 so low there. What then was the relation, in the positive and negative 

 sense, of glaciers to the two cases? The supporters of the erosion- 

 hypothesis maintain that the lake-basins were mechanically excavated 

 in the solid rock by the grinding action of the glaciers in motion, 

 working vertically. 



The first objection to this view is that lake-basins are wanting imme- 



uu2 



