The Tarns of the Canton Tieino. 705 



Soundings show a depth of 150 feet near the exit, which is a 

 narrow water-cut gorge. The lake is otherwise entirely surrounded 

 by a steep wall of rock, the lowest point in which is 718 feet above 

 the lake. It is impossible to suppose that ice has scooped out 

 this basin. The fact that springs issue from the side of the valley 

 below the lake all the year round, and that the level of the lake falls 

 26 feet below its exit in winter point strongly to solvent action. 



Of the remaining lakes scattered along the southern side of the 

 Tieino watershed, the Lago di Naret has a wedge of crystalline 

 limestone running through the centre, while the Lago Sciundrau is 

 situated on the junction of dolomite and gneiss, and the Laghetti 

 to the east of Lago di JSTaret lie along the junction of the calc- 

 schist aud the gneiss. 



The St. Got hard Lakes. — The rock-basins here also occur 

 along the line of junction of schists and gneiss. The Lago Lucendro 

 is the most important, and soundings show an axis of greatest 

 depth running along this junction. Solution does not appear to 

 have played much part in its formation. Possibly the glacier which 

 descended from Piz Lucendro has removed fragments along the 

 junction, as a transporting, not an excavating agent, as proved by 

 the soundings at the lower end of the lake. 



Lago Sella and Lago Orsino are shallow tarns which come under 

 the same category as Lago Lucendro. 



Lago d'Elio, draining into the Lago Maggiore, is due to reversal 

 of drainage by a landslip. 



These lakes, then, owe their origin, when they are rock-basins, to 

 the presence of lines of weakness, along which in many cases solution 

 has taken place, while in some shallow tarns ice may have removed 

 detached fragments ; but in no case has a lake been found which can 

 reasonably be assigned to ice-excavation independent of rock-structure. 



June 21st. — J. E. Marr, Sc.D., E.P.S., President, 

 in the Chair. 



The following communications were read : — 



1. ' The Relations of the Eocene and Cretaceous Rocks in the 

 Esna-Aswan Eeach of the Nile Valley.' By Hugh John Llewellyn 

 Beadnell, F.G.S., of the Geological Survey of Egypt. 



At the meeting of the International Geological Congress held in 

 Paris in 1900, the author brought forward evidence from the 

 Baharia Oasis and Abu Roash to show that there was a marked 

 unconformity between these two systems in the northern part of 

 the country. The Jebel-Awaina succession shows that in the 

 southern part of the country, where the Upper Cretaceous and 

 the Lower Eocene occur in their fullest development, there is no 

 sharp line of demarcation between the Cretaceous and the Tertiary, 

 and no disturbances in the stratigraphical succession. This is 

 confirmed by the succession in the Kharga Oasis, where there 

 is no trace of an unconformity. Dr. J. Ball's conclusions to the 

 contrary were mainly based on the supposed irregular variation of 

 the Esna Shales ; but, where this occurs, it is mainly due to 

 the fact that, with a slight increase of carbonate of lime, these 



