Mr. J. Ball on the Formation of Alpine Lakes, 499 



Maurice in the Valais, none certainly was borne nearly so far as 

 Villeneuve. 



Several writers on the glacial period seem to have taken it for 

 granted that very extensive glaciers must have produced streams 

 vastly more considerable than those that now flow through the 

 alpine valleys. A moment's consideration shows that this is a 

 mistake, if we admit that whatever climatal changes may have 

 occurred during the period in question were gradual and not 

 abrupt. Any other supposition would imply the sudden der 

 struction of most of the existing species of animals and plants. 

 During the period of the increase of the glaciers a part of the 

 rainfall of each year would have been converted into neve, and 

 conversely, during the period of decrease a corresponding por- 

 tion of glacier-ice would have been annually melted. The 

 streams could have been no greater than sufficient to carry off 

 the*annual rainfall, diminished in the one case, and increased in 

 the other, by the quantity gained or lost by the glacier. 



Believing as I do in the presence of the sea in the valley of 

 the Po during a portion of the glacial period, I am prepared to 

 believe that amongst the effects hitherto attributed to glaciers 

 alone, some portion may be due to the action of floating ice. 

 It seems to me highly probable that during the earlier portion 

 of that period the sea entered into the main valleys on the 

 southern side of the Alps, and that moraine-laden glaciers en- 

 tering these fiords were floated down to the open sea, where they 

 would rapidly melt, depositing their burdens at the sea-bottom. 

 At a later period it seems probable that the sea-level gradually 

 fell, while the glaciers advanced and gradually filled up the lake- 

 basins, finally depositing their moraines about the openings of 

 the greater valleys. Considering the enormous mass of mineral 

 matter brought down during this period, the operation must 

 have covered a vast extent of time ; and analogy would lead me 

 to expect that the changes of climate were not uniform. There 

 are indications of halts, during which the glaciers were sta- 

 tionary, and of oscillations that probably caused their retreat 

 and subsequent advance. The time necessary for the melting 

 of such a mass of ice as would have filled one of the great lakes 

 is so great, that it is probable that they may have been partially 

 or entirely occupied by ice after the glacier had retreated to a 

 considerable distance in the valley above the lake. 



In regard to some of the vast piles of debris that have been 

 described as moraines of extinct glaciers, and especially those 

 south of the Lake of Garda, it appears to me that a considerable 

 portion was accumulated by the stranding of ice-rafts, or masses 

 of floating glacier on the shallow sea-bottom opposite the mouth 

 of the valley. Some considerable portions of the mass are flat- 



