498 Mr. J. Ball on the Formation of Alpine Lakes. 



scarcely a ruffle on its surface. These are effects which no cur- 

 rents of running water are competent to produce. No known 

 cause, excepting the waves of the sea, or of a great lake beating 

 on a shallow bed, will spread out shingle in the fashion which 

 we see in Northern Italy. 



It is supposed that because the diluvium consists of materials 

 derived from the upper valleys of the Alps, and because it is 

 composed of waterworn fragments, it must have originally been 

 conveyed to the plain in the condition in which we see it. The 

 inference appears to me altogether unnecessary, and, for reasons 

 presently to be mentioned, very improbable. I believe ice to 

 have been the main agent for the transport of the diluvium as 

 well as the moraines, and that its waterworn character is due to 

 trituration by wave-action on a shallow shore. Besides the dif- 

 ficulty of admitting that currents descending the valleys can 

 have coated the plain with a uniform stratum of diluvium, it 

 is equally hard to understand how they can have carried the 

 diluvium across the level lake-basins, supposed to have been 

 filled up, so as to reach the plain. A slope of at least 10 feet 

 per mile, or 1 in 500, is necessary to enable a river to transport 

 rolled gravel of the size required. This objection has been per- 

 haps overstated by Lombardini, but is clearly a serious one. 

 We ought to find traces of diluvium at a great height about the 

 head of each of the greater lakes. No such traces have been 

 found. Even if great currents were able to transport and spread 

 out the diluvium as we now find it, which I cannot concede, it 

 is not easy to see how such a violent and continuous current as 

 is required can have originated in each of the alpine valleys. 

 The estimate of rainfall cannot be reasonably increased beyond 

 moderate limits ; and the greater cold of the climate, by increas- 

 ing the proportion of snow in each fall, would have tended to 

 diminish the violence of the current, and to make it more uni- 

 form in volume. The only cause likely to have acted at all has not 

 been pointed out, so far as I know. During the period of increase 

 of the glaciers, cases may probably have arisen in which a main 

 valley was barred across by a glacier descending from some 

 lateral gorge or glen ; and a lake having accumulated behind the 

 barrier, this grew until it burst its bounds, and caused a flood 

 of the same character as the well-known inundation of the 

 Dranse in 1818. But such events must have always been of a 

 local and accidental character ; it is impossible to look to them 

 for the explanation of a phenomenon so vast and so general as 

 the transport of the diluvium. In connexion with the pre- 

 ceding paragraphs, it is worth noting that the Dranse inundation, 

 the most considerable event of this kind accurately recorded, 

 does not seem to have carried any coarse debris below St. 



