182 PROF. E. J. GARWOOD ON THE [May I906, 



off of the ice, caused a diminution in the flow of the drainage in this valley, 

 and the solution of the rauchwacke gradually produced a hollow extending as 

 far as the limits of this calcareous rock. Thus at the present day, as shown 

 above, Lago Eitom is bounded on the north and north-east by steep walls of 

 crystalline schist, while its southern margin is formed by the dip-slope of the 

 underlying gneiss. The same cause may reasonably be assumed to have 

 operated in the case of Lago Tom and also of Lago Oadagno. 



In this survey of the physical history of the district, I have not 

 included the formation of the two upper lakes situated near the 

 watershed, namely Lago Scuro and Lago Taneda. These lakes 

 are, indeed, difficult to account for on any hypothesis. One fact, 

 however, appears certain, namely, that to whatever they owe their 

 existence, their occurrence along the junction of two dissimilar 

 rock-masses must have been the prime determining cause. 



III. The Lago-Tremorgio Group. 



This consists really of several groups of tarns scattered along 

 both sides of the southern watershed of the Val Levantina. They 

 lie for the most part along the outcrop of the calcareous schists, 

 in some cases exactly along the junction of these rocks with 

 the gneiss. 



Lago Tremorgio. — I will take this as a type of the lakes 

 of this group, as it is not only the largest, but, I think, the 

 most interesting, and certainly the deepest, of those occupying 

 the southern slopes of the Val Levantina. It is also one of the 

 lakes enumerated by Prof. Bonney among true rock-basins. 

 It lies at a height of 5996 feet above sea-level, and 2880 feet 

 above the Ticino. It is nearly circular in shape, having a maximum 

 diameter from north-east to south-west of 853 yards, and a width 

 at right-angles to this of 787 yards. 



The overflow escapes through a narrow waterworn notch at 

 the north-eastern corner, the lower few feet of which appear, as 

 Prof. Bonney remarks, to be artificial, and falls into the Ticino 

 by a series of cascades ; in winter, however, this stream is dry. 

 With the exception of this channel, the lake is entirely surrounded 

 by steep hillsides (see PL XIV, fig. 1). All round the southern 

 shore the lake is bounded by precipitous rocks, the upper 500 feet 

 forming an inaccessible cliff', the average slope from the water's 

 edge being 55°. The slopes from the northern and western walls 

 are gentler, but even these show an inclination of 30° to the 

 point on the northern watershed which is marked 2047 m. in the 

 Swiss Government map. 



The lake therefore lies in a funnel-shaped rock-basin, the rim of 

 which runs about 700 feet above the lake, except where it is broken 

 through at the exit : the average slope of the sides of the funnel 

 being about 45°. In fact, if we consider a funnel having this slope 

 to be tilted towards the north-west, we get an exact representation 

 of the shape of the basin. Prof. Bonney aptly compares it to an 

 armchair, which it certainly resembles, only the arms curve round 



