88 Mr. J. Ball on the Formation of 



the highest level of the ancient ice-flood, has struck every observer. 

 Where the rock is hard enough to resist subsequent degradation, 

 the eye follows the track of the former glacier as easily as it 

 traces high-water mark by the fringe of sea- weed on the shore ; 

 and if this mark avails as positive evidence of the former exten- 

 sion of glacier action, it is not less a negative proof that that 

 action did not surpass certain assignable limits. 



I shall now offer some brief remarks upon Professor Ramsay's 

 theory of the origin of alpine lakes. Although M. Mortillet 

 had anticipated Professor Ramsay in attributing the formation 

 of the lakes of Lombardy to the action of ancient glaciers, his 

 speculations on the subject are far more guarded, and at the 

 same time fall short of the generality which marks those of the 

 eminent British geologist; it is to the latter, therefore, that I 

 shall in the first place address myself. 



Professor Ramsay's argument may be summarily stated in a 

 few words. Each of the great alpine lakes lies in an area once 

 covered by glacier; no satisfactory explanation of the origin of 

 alpine lakes has yet been given ; the glacier considered as a 

 mechanical agent is competent to scoop out the rock basins in 

 which the alpine lakes generally lie ; therefore, the lakes have 

 been formed by glaciers. 



The first of these propositions, even though it be admitted 

 with some reserve, does not hold inversely, as it should do if the 

 scooping out of rock basins were one of the natural functions 

 of glaciers. Why should not the glacier that flowed from Susa 

 to beyond Turin, or the still vaster mass that descended from 

 the Val d'Aosta, excavate a basin as deep and large as the Lago 

 Maggiore or the Lake of Como ? Why throughout the Dauphine 

 Alps, or the far more extensive region of the Tyrolese, Salzburg, 

 Carinthian and Styrian Alps, are no lakes found in the path of 

 the great extinct glaciers ? Again, in admitting the proposition 

 in its direct form, it is necessary to draw a marked distinction 

 between the assertion that the existing lakes lie within an area 

 once covered by glacier, and the fact that some of them lie in 

 valleys which once gave passage to the main stream of an extinct 

 glacier. Even though the efficiency of the glacier as an exca- 

 vating tool were demonstrated, instead of being, as I feel sure, 

 capable of disproof, it is not easy to conceive how it could have 

 been applied to the hollowing out of such basins as the Lake of 

 Lugano or the Lake of Zug. The mountain-valleys that are 

 drained into the former lake are of the most trifling dimensions, 

 and their height relatively insignificant. The main supply of 

 ice to the basin of the lake was, on the one hand, from the glacier 

 of the Adda, then occupying the site of the Lake of Como, across 

 the ridge between Menaggio and Porlezza, and, on the other, 



