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



he adds the remark that, according to this theory, the transverse 

 valleys must be more ancient than the longitudinal ones, which 

 explains the bend made by the Rhone at Martigny. 



Before seeking for a solution of the problem of the lakes, it 

 appears to be necessary to examine more closely the effects of 

 erosion, which in all the proposed solutions plays an important 

 part. It holds the first place in those of Professors Ramsay and 

 Tyndall, and the second in those of MM. Desor and Mortillet. 



No one doubts that erosion has played a great part in the 

 configuration of the valleys and depressions of mountainous 

 countries. When, in our Molassic regions, in Appenzell, in the 

 Emmenthal, and in the neighbourhood of Berne, Fribourg, and 

 Lausanne, we see horizontal or slightly inclined strata cut by 

 large and small valleys ramifying into gorges and ravines which 

 date, so to speak, from the last storm, — when in districts in 

 which the ground is schistose, such as the Simmenthal, certain 

 parts of the Grisons or the Valais, or the woodless mountains of 

 Savoy and Dauphine, we see each fall of rain give rise to new 

 falls of rock, — lastly, when we consider the great masses of de- 

 bris which from the most remote periods have been transported 

 beyond the mountains by the glaciers and rivers, — it seems im- 

 possible to estimate too highly the influence which the constant 

 action of erosion must have exercised upon the conformation of 

 the country. It is certain that many of our valleys owe to it 

 their origin, and nearly all their present characters. Neverthe- 

 less there is a limit which the erosive action of rivers and glaciers 

 does not exceed, and which depends upon the resistance of the 

 bottom, the mass of water or ice, and upon the slope. This 

 limit being attained in favour of the resistance, by the solidity 

 of the bottom or by the diminution of the mass of water or of 

 the slope, the rivers, instead of continuing the erosion, fall in 

 cascades and cataracts, or seek issues which present fewer obsta- 

 cles, or, if their rapidity permits, they form deposits. From time 

 immemorial the falls of the Rhine, the Toccia, and the Aar, and 

 the cataracts of the Rhine at Laufenburg and those of the 

 Danube and the Nile, have not changed either in place or form. 

 When thus we see a river traverse solid rocks, such as compact 

 limestones, granites, or porphyries, whilst at the same level it 

 might have cut itself a way through softer rocks, we must be 

 convinced that its course has not been impressed upon it by 

 erosion. The Rhine near Sargans had to surmount an elevation 

 of only twenty feet above its highest level in order to throw 

 itself in a straight line into the Lake of Wallenstadt ; why then 

 should it have taken its course, making a bend and traversing 

 the calcareous mountains of the Schollberg and Flascher Berg, 

 if these mountains had not offered it a more ready passage, of a dif- 



