THE 



LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. XXVI. FOURTH SERIES. 



LXX. On the Formation of Alpine Lakes. 

 By John Ball, M.R.I.A., F.L.S.* 



TWO distinguished Italian geologists, MM. B. Gastaldi and 

 G. de Mortillet, have recently published letters f in which 

 they seek to controvert the objections which have been raised to 

 the theory of the formation of alpine lakes first published in 1859 

 by the last-named writer. 



M. de Mortillet devotes some pages of his letter to the 

 discussion of objections to his theory incidentally urged by me 

 in a paper published in this Journal in the month of February 

 last. The immediate object of that paper was to controvert views 

 respecting the former extent of glacial action which had been 

 advanced in this country by Professors Tyndall and Ramsay; 

 and to that portion of my argument I understand that both 

 writers give their assent. Neither they, nor, so far as I know, 

 any other of the Swiss or Italian geologists who have studied 

 this question, believe with Professor Tyndall that glaciers have 

 been the main agents in the formation of alpine valleys, nor 

 with Professor Ramsay that they are competent to excavate the 

 deep rock basins, or troughs, that now contain the lakes of the 

 Alps. 



As the few observations which I made with reference to 

 M. de Mortillet's theory have been evidently misapprehended 

 by that gentleman, I am anxious to state rather more fully the 

 objections which I have to advance, together with some evidence 

 bearing on the subject that I have recently obtained. 



The broad facts as to which there is a general agreement 

 amongst those who have discussed this subject are as follows : — 



1. The low country at the south side of the Alps, extending 

 about 240 miles from the Isonzo to the west of Piedmont, is 

 covered with a deposit of rolled stones, gravel, and sand, which 

 has been generally called diluvium, but to which M. de Mortillet 

 gives the name ancient alluvium. 



* Communicated by the Author. 



t In vol. v. of Atti delta Societa Italiana delle Scienze Naturali. 

 Phil. Mag. S. 4. No. 178. Suppl. Vol. 26. 2 K 



