98 Mr. J. Ball on the Formation of 



the primary ridges and furrows which mark the earlier corruga- 

 tions of the surface. 



In considering the mechanical effects of lateral compression 

 applied transversely to the direction which has caused the earlier 

 and predominant flexures of the surface, we are led to speculate 

 on the probability of fracture owing to the inability of the ridges 

 to yield to the necessary extent in a new direction. The actual 



Fig. 3. 



occurrence of such fractures would depend upon the plasticity 

 of the materials ; but the summit of each convex flexure would 

 necessarily sustain a tension competent under given conditions 

 to cause rupture. It can scarcely be by an accident that the 

 annexed figure, which appears to be an ideal illustration, does 

 actually represent, in a rude fashion, the main ridges and trans- 

 verse valleys of western Switzerland and northern Savoy. If 

 the lines A A 1 , B B 1 , C C 1 , and D D 1 be taken to represent the axes 

 of elevation of the Jura and the chief ranges of the Alps, the 

 reader will have no difficulty in identifying in the short longi- 

 tudinal lines the valley of Chambery from Montmelian to Culoz, 

 the valley of the Cheran, that of Annecy, the gorge of the Isere 

 between Albert ville and Montiers, the defile of Maglan, the 

 valleys of Montjoie, Bonneval, and Tignes, the Val d'Entremont, 

 and that of the Rhone from Martigny to Vevay, the Eringer 

 Thai, Einfisch Thai, Saas Thai, the pass of the Simplon, the 

 Valley of Hash, the Valley of the Reuss, &c. It will not escape 

 notice that nearly all the transverse valleys above enumerated, 

 and many others of less importance that might be added to the 

 list, are wholly or in part narrow defiles. There can be no doubt 

 that water and ice have contributed largely to give them their 

 present form ; but the same causes have acted elsewhere without 

 producing the same general character of valley. 



This is not the occasion on which to attempt to apply in 



