Yol. 62.~] TAKNS OF THE CANTON TICINO. 171 



water does not reach the channel, and a broad, flat beach is laid 

 bare at the south-western end of the lake ; the spring, however, 

 continues to issue at the same spot. This 'terminal' wall of 

 rauchwacke is rotten and honeycombed, and just above the spot 

 where the spring now issues is situated a large cave which evidently 

 represents the old source of the spring, when it escaped higher in 

 the rauchwacke (see PI. XII, fig. 1). Apparently it has gradually 

 dissolved its way down to the level of the insoluble schist, against 

 which it is now thrown out. The rock is a fine-grained meta- 

 morphosed limestone containing some 16 per cent, of dolomite, and 

 8 per cent, of insoluble material, chiefly silica. 



The bathymetrical chart (PI. XVII) shows the general shape of 

 the lake-floor. The maximum depth of 50 feet is situated about 

 one-third of the way from the northern end of the lake. The axis of 

 greatest depth runs east and west, and passes through this point. It 

 is parallel to the strike of the rocks, and appears to coincide with 

 the junction of the rauchwacke and the overlying crystalline 

 schist. The shore of the lake is entirely formed of delta-material 

 and sand, with the exception of the southern wall of rauchwacke 

 described above. .But for this the upper end of the lake would, as 

 in the case of Lago Eitom, undoubtedly show deeper soundings near 

 the northern shore. The flat shallow bay occupying the southern 

 end between the delta and the exit-channel has an average depth 

 of about 3 feet, and is strewn with fragments of minerals, many of 

 them presumably derived from crystalline schists. These coarser 

 fragments must have been brought down by the stream descending 

 between the rauchwacke and the overlying schists ; and it is a very 

 suggestive fact that, although fragments of mica clearly derived 

 from the rauchwacke are represented, no pebbles of this rock are 

 found, despite its occurrence here in situ round the end of the lake. 



Lago Cadagno (see Pis. XI & XVIII) lies due east of Lago 

 Tom, at the somewhat lower level of 6302 feet. It is situated 

 apparently on the strike of the same beds (namely, the rauchwacke 

 on the south, and the overlying crystalline schists on the north), and 

 occupies a slight synclinal depression. It is surrounded by alluvium 

 and scree-debris, with the exception of the north-eastern corner, 

 where solid rock occurs, and the southern bank, where the rock is 

 plastered with morainic material. The lake doubtless once extended 

 to the rocky barrier over which the river now falls into Lago 

 Eitom ; but the western end has been rilled up by material washed 

 down from the steep escarpment on the north and north-west. It 

 is possible that it once drained from its south-eastern end. The lake 

 is 875 yards long and about 330 yards in width, the greatest depth 

 being 62 feet. The bathymetrical chart (PI. XVIII) shows that it- 

 is a symmetrical spoon-shaped hollow, having an axis of greatest 

 depth running east and west, parallel to the length of the lake, 

 situated nearer to the northern than to the southern shore. It is 

 fed by a group of some ten or twelve streams which cascade down 

 the precipitous scarp-face on the north. Most of these originate in 



