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496 Mr. J. Ball on the Formation of Alpine Lakes* 



The fact that the bed of 

 shingle seen through the 20$ s/s 1&1 10s 

 clear water shelved very gra- 

 dually from the shore, and 

 the results of the two first 

 soundings, appeared to my- 

 self and my companion con- 

 firmatory of M. de Mor- 

 tillet' s assertion, whatever 

 the explanation of the fact 

 might be. But the two suc- 

 ceeding soundings, coupled 

 with the fact that at a short 



distance (less than 10 yards) further from the shore no bottom 

 was found with 370 feet of line, proved to demonstration that 

 the subaqueous precipice is continued along the S. face of the 

 promontory, and that the objection originally taken by me sub- 

 sists in all its force. I may remark that by following along the 

 shore to the S.W., towards the hamlet of Campo, any one who 

 may repeat the observations will approach the mouth of a stream 

 which, like every other torrent falling into the lake, pours into it a 

 mass of detritus that doubtless forms a conical mound beneath the 

 level of the lake, not to be confounded with the ancient diluvium. 



With the help of the annexed diagram the explanation of the 

 fact noted by M. de Mortillet is sufficiently obvious. On all 

 the more level spots surrounding the lake, extending from the 

 shore to a height of about 2000 feet, deposits of unrolled or 

 partially waterworn materials are to be found. These deposits 

 are formed from rocks existing in situ in the alpine valleys 

 surrounding the head of the lake, and were doubtless conveyed 

 by ice to the spots where we now find them. Whether originally 

 waterworn or not, a deposit of such materials exposed for ages 

 to the action of the water on the lake-shore would necessarily 

 be reduced to the condition in which the small shingle-bank in 

 question was detected by the keen eye of M. de Mortillet, and 

 pressed into service as a witness for his theory. 



I shall naturally be asked by some who may have followed me 

 so far, what explanation I have to offer of the relations between 

 the diluvium and the more recent glacial phenomena on the 

 south side of the Alps to which M. de Mortillet has called 

 attention. To this I reply that a complete answer cannot, as 

 I believe, be given until the whole of the facts shall have been 

 minutely studied with a degree of care that has not yet been 

 applied to them, and which indeed would not have been prac- 

 ticable until the nature of the problems to be discussed was 

 somewhat defined. 



