Reports and Proceedings — Geological Society of London. 335 



in the Canton Ticino. Most of these drain into the Ticino basin ; 

 one or two, however, flow into the Eeuss or the Ehine. 



Val Piora Lakes. — These are chiefly rock-basins which lie in all 

 cases along the junction of two dissimilar rock -masses. Detailed 

 soundings prove that the axes of greatest depth of the lakes coincide 

 with these lines of junction : one side being a dip-slope, the other 

 an escarpment. It is shown that in the case of three of the larger 

 lakes soluble calcareous beds have been brought by thrusts against 

 crystalline rocks. 



The origin of the lakes cannot be attributed to ice-excavation, as 

 the ice must not only have invaded the district from outside, but 

 must also have come from several different directions at once. 

 Other difficulties in the way of accepting this mode of origin are 

 also pointed out. 



They appear to be due to structural peculiarities of the district, 

 aided by solution. Analyses of the rauchwacke are given, and its 

 characters are described. 



The lakes appear to be connected with a reversal of the drainage 

 of the Piora Valley, consequent on the over-deepening of the Val 

 Levantina in Interglacial times and the elevation of the upper end 

 of the district as the ice-cap melted away. 



Two of the other lakes of this group lie on or near the watershed : 

 their origin is difficult to account for, except by differential weathering 

 along the lines of junction. 



Lago Tremorgio Group. — These tarns are all situated either on 

 the calc-mica-schists or on outcrops of crystalline limestone and 

 dolomite. Lago Tremorgio itself is almost certainly due to solution. 

 A typical analysis of the schists gives 75 per cent, of calcium- 

 carbonate. This occurs chiefly in the form of eyes of granular 

 calcite which crumble between the fingers, and is found to be 

 dissolved out in the submerged rock, while sharp reefs run out 

 under water. 



Soundings show a depth of 150 feet near the exit, which is a 

 narrow water-cut gorge. The lake is otherwise entirely surrounded 

 by a steep wall of rock, the lowest point in which is 7l8 feet above 

 the lake. It is impossible to suppose that ice has scooped out this 

 basin. The fact that springs issue from the side of the valley below 

 the lake all the year round, and that the level of the lake falls 

 20 feet below its exit in Winter, points strongly to solvent action. 



Of the remaining lakes scattered along the southern side of the 

 Ticino watershed, the Lago di Naret has a wedge of crystalline 

 limestone running through the centre, while the Lago Sciundrau is 

 situated on the junction of dolomite and gneiss, and the Laghetti to 

 the east of Lago di Naret lie along the junction of the calc-schist and 

 the gneiss. 



The St. Gothard Lakes. — The rock-basins here also occur along 

 the line of jimction of schists and gneiss. The Lago Lucendro is 

 the most important, and soundings show an axis of greatest depth 

 running along this junction. Solution does not appear to have 

 played much part in its formation. Possibly the glacier which 

 descended from Piz Lucendro has removed fragments along the 



