84 Mr. J. Ball on the Formation of 



and, when taken together, bring to my mind the conviction that 

 some considerable portion at least of the existing valleys in the 

 Alps owe their origin to forces which have operated on a great 

 scale, and which can scarcely be any other than those that have 

 raised the mountain ridges to which the same valleys are related. 

 If it be urged that several of the valleys to which I have referred 

 lie along the line of outcrop of softer and more easily disinte- 

 grated rocks, such as certain slates in the valley of the Rhone, 

 and that the action of either water or ice would for that reason 

 be more effective in scooping out the valley where we now see it, 

 I may reply that the very fact alleged shows the working of 

 denudation along the same line at some early period in the 

 history of the elevation of the Alps, and the strong probability 

 of the existence at the same period of a corresponding valley. 



If we now pass from the contemplation of a wide tract of 

 mountain country to the examination of particular groups or 

 massifs, we very frequently find indications of the prevalence of 

 a common direction in the secondary ridges and valleys, trans- 

 verse, but seldom exactly perpendicular, to that of the main 

 valleys. Thus in the Bernese and Lepontine Alps we find the 

 ridges enclosing the two main branches of the Aar Glacier, those 

 on either side of the Geren Thai, the Val Leventino between 

 Airolo and Faido, and several minor valleys, all showing a 

 degree of parallelism which points to the operation of some 

 common cause. The series of seven minor valleys lying about 

 due east and west between the Val Maggia and that of the Tosa 

 is perhaps a better illustration, as there is nothing in the gene- 

 ral configuration of the district to make it conceivable that, if 

 the hollows were filled up, water or ice would reopen trenches 

 where the present valleys exist. The four or five great ridges 

 extending northwards from the range of Monte Rosa towards 

 the valley of the Rhone furnish, as I believe, another illustration 

 of the same tendency to the formation of groups of parallel 

 valleys. 



The facts hitherto adduced seem to me to point very strongly 

 to the conclusion that mechanical forces, acting on a large scale 

 and in definite directions, have had at the least a considerable 

 share in the formation of alpine valleys. For reasons to which 

 I shall further advert, it appears most probable that complicated 

 forces acting on the mountain masses have given rise to many 

 valleys whose direction gives no clue, or none that has yet been 

 traced, to their origin ; but I am quite ready to admit that the 

 present condition of the surface cannot readily be explained with- 

 out very largely admitting the action of water, whether in the 

 liquid or solid form. To study the various agencies that, some- 

 times working together, sometimes in alternation, have given to 



