18 Professor T. G. Bonney — Lake-hasins in the Alps. 



below that of the lake. Hence, even if the latter to some extent is 

 retained by drift, it may nevertheless, since it is not very shallow, 

 be claimed as a rock-basin. 



A short distance from the Lago Cadagno, the level of the 

 valley, as already stated, is interrupted by cliffs and craggy steep 

 slopes, at the bottom of which lies the basin of the Lago Ritom, 

 in shape something like a shortish straight sausage. The part 

 occupied by water is rather more than two thousand yards in 

 length, and on an average about a quarter of the width ; ^ the upper 

 end, now a grassy meadow traversed by streams, is rather less than 

 a thousand yards long. The basin is bounded on the southern side 

 by a range of gneiss — forming here the northern boundary of the 

 Val Bedretto — which descends with moderate steepness to the lake, 

 and slightly indents the margin of the latter with the openings 

 of its shallow valleys. Steep grass slopes and crags of micaceous 

 schist, becoming more precipitous towards the north, form the head 

 of the basin, and a line of crags, at about the same elevation, 

 extends nearly to the lower end of the delta, where they are merged 

 in the steep slope. The basin, indeed, is bounded on all the 

 northern side by steep grass slopes and high cliffs, outposts of the 

 central range of the Lepontine Alps. The part visible from below 

 .consists of the dark micaceous schists,^ already mentioned. The 

 lake-basin, in fact, lies obliquely across the zone of these rocks ; its 

 upper end being not far from their northern boundary, its lower 

 just at the southern limit. As this is approached, the slopes con- 

 tinue steep ; the schists pass away across a range towards the lower 

 end of the Val Canaria ; the lowest part of the crest, where also 

 some rauchwacke occurs, lying between the Plan Alto (7,428 feet) 

 and Fongio (7,257 feet), perhaps four or five hundred feet below 

 the latter. This mountain is chiefly composed of gneiss, and is in 

 reality a prolongation of the gneissic range which, as already 

 mentioned, forms the southern bank of the Lago Eitom. There the 

 valley in which that lake lies makes at this point a sharp turn to 

 the south, and the water is discharged through a very narrow glen 

 — a mere gateway in the mountains ; for within a few yards of the 

 foot of the lake the stream leaps down towards the Val Bedretto 

 in a grand series of cascades. This is practically unbroken 

 for some hundreds of feet, since the craggy slope is extremely steep 

 to below the hamlet of La Valle. At the above-named gateway, close 

 to the Hotel Piora, rock can be seen on either side of the stream, 

 obviously forming its bed. A glance at the mountains on either 

 side shows the existence of any other outlet to be impossible. So 

 the Lago Eitom must occupy a true lake-basin, and that a fairly 

 deep one. 



1 Professor Forel has kindly informed me that it is 2,000 metres long, 600 metres 

 ■wide, and 60 metres in greatest depth. I am indebted to him for the measurements 

 of Lago Cadagno and Tom. 



- They belong to the group 'which for purposes of reference I have called the 

 Upper Schist. They are described, as well as the geology of the Val Piora, in the 

 Quart. Journ. Geol. Soc, xlvi (1890), p. 199, etc. 



