102 On the Formation of Alpine Valleys and Alpine Lakes. 



these the effects of denudation on an immense scale, and the 

 minor, but still important, mechanical action of water and ice, 

 and it is not surprising if many difficulties long remain unsolved. 

 At present the important point is to find the true clue through 

 the labyrinth. Of some of the main difficulties in alpine stra- 

 tification, and especially of what has been called the fan structure, 

 I think that the hypothesis here advanced gives a better explana- 

 tion than any other that I know. The final decision may probably 

 await more minute and persevering study of the structure of the 

 Alps than has even yet been given, although the names of great 

 geologists, deceased or still living, seem to contradict the sug- 

 gestion. 



The hypothesis of lateral compression, in the form in which it 

 presents itself to my mind, is absolutely inconsistent with the 

 maxims of the cataclysmal school of geology. If mountain 

 chains owe their elevation to the gradual cooling of the earth, it 

 is a flat contradiction of the laws of physics to infer, as an Ame- 

 rican writer has done, the possibility of the sudden elevation of 

 a mountain a mile in height, or even an incomparably less 

 amount of rapid disturbance. More cautious reasoning should 

 lead us to expect that the vertical disturbances would be abso- 

 lutely insensible, but that the lateral displacements, encounter- 

 ing greater and more unequal resistance, might sometimes cause 

 sensible effects. Whether we may here find a cause of earth- 

 quakes, indirectly connected with the elevation of certain moun- 

 tain chains, is a question which I am not now prepared to discuss. 



It is scarcely necessary to advert to exceptional causes which 

 may have operated in the formation of certain mountain-valleys. 



For instance, in the Eastern Alps there seems reason to sup- 

 pose that the chemical changes which led to the formation of 

 dolomite were accompanied by contraction in the mass of corre- 

 sponding portions of the Jurassic rocks, causing irregular cracks 

 and fissures, which, enlarged by marine action, have produced 

 the irregular disposition of the valleys, and the characteristic 

 forms of the peaks in that district. 



To conclude, I am persuaded that there is no single valley of 

 the Alps that does not owe its present form in great part to the 

 action of glaciers, and it is a great gain that all the modes of 

 action of this powerful agent should be fully studied ; but, while 

 believing that the main features of the surface have originated in 

 more general causes, I feel surprise that Professor Tyndall has 

 not referred more pointedly to another agent which has surely 

 had even a larger share than that of glaciers in fashioning the 

 great alpine masses. He rightly rejects running water as a 

 means of extensive excavation, but he does not seem to have 

 considered the effects of long-continued marine action upon steep 



