Vol. 62.] THE TATCtfS OF THE CAXTON TICINO. 187 



the north, while the smaller tarns are obviously dammed by loose 

 material. 



Lago della Sella. — This lake forms an irregular sheet of water 

 lying in the Yal Torta, east of Monte Prosa, at a height of 7320 

 feet. It consists of a shallow lake on the north and a smaller 

 pond on the south, united by a rocky ditch about 180 yards long, — 

 the whole giving the idea of a Hooded river-system (see PL XY, 

 fig. 2). The actual exit is dammed by a landslip, although the 

 lower sheet is certainly a rock-basin. The northern and western 

 shores of the main lake are formed of gneiss, while biotite-schist 

 occupies the southern and eastern banks. This schist resembles 

 that which forms the northern bank of Lago di Lucendro, and is 

 penetrated by similar granite-veins. 



The strike of the schist is north-east and south-west, parallel with 

 the longer axis of the lake, the dip being some 60° north-westward. 

 The schist forms a rocky ridge running into the southern end of 

 the lake. This rises to the surface again in two islands, united 

 under water by shallow depressions only 12 feet deep. Five rows 

 of soundings were run across various portions of the lake, but the 

 presence of the islands made a systematic survey difficult in the 

 absence of a boat. The greatest depth met with was 25 feet, though 

 it is possible that greater depths may exist near the upper end of 

 the lake. The origin of the lake, however, seems to be due to 

 precisely the same causes as Lago di Lucendro, namely, a line of 

 junction between gneiss and biotite-schist along which unequal 

 weathering has taken place, the more weathered portions having 

 been removed by the ice, which must once have gathered in the 

 Val Torta and flowed over the district, now occupied by the lake. 

 It is noteworthy, in this connection, that the stream now flowing 

 into the lake from the Yal Torta runs for. over a mile exactly along 

 the junction of the gneiss and the schist. 



V. The Lago d'Elio. 1 



Although situated just beyond the political boundary, this lake 

 belongs geographically to the Ticino basin. It lies at a height of 

 3025 feet, or 2378 feet above the Lago Maggiore, and is situated on 

 the watershed between the Val Molino and the Yal Yedasco. It 

 occupies an elongated triangular depression in the gneiss between 

 Monte Borgna and Monte Cadrigna. The lake has a length of 930 

 yards from north-north-east to south-south-west, and a width at the 

 upper end of 300 yards, which forms the base of the triangle : from 

 here it gradually tapers to the exit, which lies in the acute angle of 

 the triangle at its southern end. The deepest soundings were met 

 with about one-third of the distance from the upper end, the 

 greatest depth being 134 feet, while depths of 74 and 75 feet were 



1 A batlrymetrical chart of this lake has been constructed ; but it is 

 unnecessary to introduce it here, as the lake has not been proTed to be a rock- 

 basin. 



