168 PROP. E. J. GARWOOD Otf THE [^ a J 1906, 



II. The Lakes of the Yal Piora. 

 [PI. VII — topographical map, facing this page.] 



These lakes lie in a series of hollows in and around the mountain- 

 glen of the Val Piora. This depression has been carved out of a 

 series of limestones and schists, which have been squeezed in 

 between two masses of gneiss — one of these forming the northern 

 wall of the Val Levantina below Airolo, and the other constituting 

 the Val-Cadlimo district on the north. That the majority of these 

 lakes occupy rock-basins is clearly shown in Prof. Bonney's careful 

 description. 1 I will reserve any further general remarks until 

 I have described the lakes in detail, when we shall be in a better 

 position to discuss the evolution of the district as a whole. 



Lago Bitom (see Pis. VII, VIII, & XVI) is situated exactly 

 6000 feet above sea-level, and occupies a true rock-basin. It has 

 a length of about 2190 yards, and a width (at the upper end) of 

 some 590 yards, becoming narrower towards the exit. It is fed 

 chiefly by three streams, namely, the Murinascio torrent, draining 

 the Val Piora, and the two streams carrying the overflow from 

 Lago Tom and Lago Cadagno respectively. These last-named lakes 

 receive the drainage from two unnamed tarns, to which, for conve- 

 nience, I shall refer as Lago Taneda and Lago di Murinascio. The 

 former (namely, Lago Taneda), which lies on the watershed, drains 

 southwards through the Lago Cadagno. Lago di Murinascio has 

 no true exit ; any surplus-water that there may be finds its way 

 through the screes which form the lowest point of its containing 

 barrier. Lago Eitom must once have extended nearly 1000 yards 

 farther to the north-east, over the area now occupied by a delta 

 which forms a swampy alluvial flat ; a delta which, from its 

 peculiar situation, might well be used to ascertain the length of 

 time that has elapsed since the close of the Glacial Period in this 

 district. The southern shore of the lake is formed of coarse foliated 

 gneiss, dipping north-north-westward at about 35°; while the 

 northern bank runs along the foot of a steep escarpment of 

 calcareous crystalline schists — a complicated series, much folded, 

 contorted, and crushed. At the south-eastern corner of the delta, 

 outcrops of rauchwacke and dolomite occur ; and the same beds 

 must form the floor of the lake throughout its length, for they 

 reappear at its western end, where they are found cropping out 

 close to the Hotel, while beds of a similar calcareous character 

 occupy most of that end of the lake in places up to the 1980-metre 

 contour. As this fact is not at all clear from Dr. K. von Pritsch's 

 map, where only a small patch of rauchwacke is shown, forming 

 the saddle between Pian' Alto and Pongia, a brief description of 

 the rocks that occupy this end of the lake is necessary. 



Starting from the exit of the lake, we find the water of the Poos 

 running out over the southern mass of gneiss. This rock can be 



1 Geol. Mag. 1898, pp. 15 et seqq. 



