Vol. 62.] TAHNS OF THE CANTON TICINO. 179 



flowed out of the lakes. These are found to contain total 

 solids : — 



Lago Tom "0733 gramme per litre. 



Lago Cadagno "1260 „ „ 



A qualitative analysis showed that the solid salts consisted of 

 lime and magnesia, with a little iron and alumina. In the case of 

 Lago Cadagno especially, a great deal of sulphuretted hydrogen 

 was discharged when the mud was disturbed on the bottom of the 

 lake, and the sounding-line and plummet, when drawn to the shore, 

 always smelt strongly of this gas. The same phenomenon was 

 noticeable in the case of Lago Bitom, but I never noticed the 

 presence of sulphuretted hydrogen in the mud from the floor of 

 Lago Tom. 



There can be little doubt, I think, that the presence of this gas 

 in such quantities in the deposits of Lago Bitom and Lago Cadagno, 

 and its absence from Lago Tom, must be attributed to the presence 

 of nshes in the two former lakes and their absence from the last- 

 named. "While the two former are stocked with trout, all attempts 

 to rear trout in Lago Tom have failed, and this failure is attributed 

 by M. Lombardi to the presence of lime in its waters. 



[In this connection the investigation of MM. Andre Delebecque 

 & Ernest Bourcart on the waters of certain Alpine lakes is full of 

 interest. 1 M. Bourcart finds in the bottom-waters of Lago Bitom 

 2*365 grammes of dissolved salts per litre, including the following 

 salts : — 





Grammes. 



Si0 2 



= o-oio 



CaO 



= 0-737 



MgO 



= 0-1962 



so 3 



= 1-3767 



K 2 



- 0-0042 



Na o 



= 0-0027 



Fe 2 Al a 3 



= 00012 



The surface-water, on the other hand, contains only 0*140 gramme 

 per litre of dissolved salts ; and the three affluent streams from 

 Lago Tom, Lago Cadagno, and the Val Piora contain a mean of 

 0-139 gramme per litre (op. cit. p. 937). 



The authors are probably right in concluding that the great 

 increase in dissolved salts found in the bottom-waters is due to 

 underground springs, which enter the lake through the soluble 

 rauchwacke. It might be urged that the salts had accumulated 

 at the bottom by degrees, owing to the formation of ice in winter 

 and the consequent concentration of the salts in the surface-water, 

 which would thus have its specific gravity increased, and, being at 

 the same time cooled down, would be compelled to descend. An 

 interesting point in this connection is, however, brought out by 

 the temperature-determinations made by these authors at different 



1 Comptes Renclus Acad. Sci. Paris, vol, cxxxix (1904) pp. 936 et seqq. 



