Prof. B. Studer on the Origin of the Swiss Lakes, 487 



ferent and more ancient origin ? Why should the Simme near 

 Wimmis have forced a passage through the limestones of the Burg- 

 fluh, when between the latter and the Niesen there were only- 

 schists to be traversed ? Why should the Sarine have hollowed 

 out its channel by the long limestone defile from Rossiniere to 

 Montbovon, when to the left there was the depression of the 

 Mosses, of which the Flysch rock presented much less resistance? 

 The impossibility of explaining by erosion those ravines which 

 are evidently large crevasses, as also the relation existing between 

 the longitudinal valleys and the strike and dip of the strata, are 

 facts long since established in science. They have set up the 

 conviction that the forces of erosion have not acted alone, but 

 that other very powerful agents have modified and fashioned the 

 surface of the globe. It is half a century since this result was 

 indicated in this same journal by a distinguished physicist*. In 

 all treatises on geology the origin of each of the different kinds 

 of valleys is deduced from a particular principle. 



The reasons which show us the insufficiency of the erosion by 

 rivers to explain the origin of a great number of valleys, acquire 

 much more force in Mr. BalPs excellent memoir if we apply them 

 to glaciers, the effects of which are comparable to those of streams 

 of lava. If the latter possessed the power of working up the 

 soil over which they pass, which is often composed of moveable 

 sand and but slightly coherent tuffs, as it is asserted that the 

 glaciers do, the physiognomy of volcanic cones and districts 

 would be very different from that which we know to belong to 

 them. As in the case of lavas, the retardation of the movements 

 of glaciers upon their bottom is necessarily much greater than 

 with streams of water. Upon the heights, when the mean tem- 

 perature is below zero (C), the ice even remains attached to the 

 soil, and the glacier, if it can be formed, only advances at its 

 upper part ; but in general the new-fallen snow glides over the 

 solid ice, forming avalanches, and the glacier, remaining unthick- 

 ened, advances, notwithstanding its often considerable slope, 

 much more slowly than the very large glaciers of the valleys. 

 The latter can hardly exert any very active erosion, their lower 

 surface being often separated from the beds by the water arising 

 from their melting, or by empty spaces, and their movement 

 being far less than that of rivers which appear to us to be stag- 

 nant. Nevertheless a certain amount of erosion takes place, as 

 is proved by the turbid water which issues from the glaciers ; but 

 its action appears to be limited to rounding off points and 

 salient angles, and polishing and striating the rocks. One of 

 the best ascertained facts is that the erosion of glaciers is distin- 

 guished from that of water by the production by the former of 

 * Bibl, Brit, vol. lix. 



