704 Geological Society: — 



anhydrous silicates into serpentine, the authors embody their inves- 

 tigations in the following conclusions : — 



(1) That both a tint and pleochroism are accidental rather than 

 essential characteristics of antigorite. 



(2) Neither are low polarization-tints characteristic, unless two 

 mica-like minerals exist, otherwise indistinguishable. 



(3) That it is doubtful whether any hard-and-fast line can be 

 drawn between antigorite and the more fibrous forms in ordinary 

 serpentine-rocks. 



(4) That the most typical antigorite appears when the rock has 

 been considerably affected by pressure, but it becomes less so when 

 the latter has been very great. 



(5) That so far from the nearly -rectangular cleavage of augite 

 originating the ' gestrickte struktur,' it is worse preserved than 

 any other original one in the process of serpentinization. Typical 

 antigorite, however, apparently is rather more readily produced from 

 augite than from the other ferromagnesian silicates, but is more 

 directly a consequence of pressure than of chemical composition. 



2. ' The Tarns of the Canton Ticino.' By Prof. E. J. Garwood, 

 M.A., Sec.G.S. 



The lakes dealt with comprise the larger Alpine tarns which 

 occur in the Canton Ticino. Most of these drain into the Ticino 

 basin ; one or two, however, flow into the Reuss or the Rhine. 



Yal-Piora Lakes. — These are chiefly rock-basins which lie in 

 all cases along the junction of two dissimilar rock-masses. Detailed 

 soundings prove that the axes of greatest depth of the lakes coincide 

 with these lines of junction: one side being a dip-slope, the other 

 an escarpment. It is shown that in the case of three of the larger 

 lakes, soluble calcareous beds have been brought by thrusts against 

 crystalline rocks. 



The origin of the lakes cannot be attributed to ice-excavation, as 

 the ice must not only have invaded the district from outside, but 

 must also have come from several different directions at once. 

 Other difficulties in the way of accepting this mode of origin are 

 also pointed out. They appear to be due to structural peculiarities 

 of the district, aided by solution. Analyses of the rauchwacke are 

 given, and it characters are described. 



The lakes appear to be connected with a reversal of the drainage 

 of the Piora Valley, consequent on the over-deepening of the Val 

 Levantina in Interglacial times and the elevation of the upper end 

 of the district as the ice-cap melted away. 



Two of the other lakes of this group lie on or near the water- 

 shed : their origin is difficult to account for, except by differential 

 weathering along the lines of junction. 



Lago-Tremorgio Grou p.- — These tarns are all situated, either 

 on the calc-mica-schists, or on outcrops of crystalline limestone and 

 dolomite. Lago Tremorgio itself is almost certainly due to solution. 

 A typical analysis of the schists gives 75 per cent, of calcium- 

 carbonate. This occurs chiefly in the form of eyes of granular calcite 

 which crumble between the fingers, and is found to be dissolved 

 out in the submerged rock, while sharp reefs run out under water. 



