Alpine Valleys and Alpine Lakes. 99 



detail the principles here advocated, nor do I pretend to have 

 the requisite amount of special knowledge. They appear to me 

 to account for a large number of the broader facts of general 

 orography, and more especially for many of the peculiarities in 

 the conformation of the Alps that have attracted the attention 

 of geologists. Of the former class I may instance the almost 

 continuous zone of mountains that traverse the eastern hemi- 

 sphere between the 30th and 50th parallels of latitude, through- 

 out which the prevailing tendency of the ridges approaches to 

 parallelism with the equator, together with the general tendency 

 towards a meridional direction in the ranges N. and S. of that 

 zone. 



Of the leading facts of alpine orography which find their 

 explanation in the development of the views here propounded, I 

 would in the first place note the connexion between the principal 

 peaks and the secondary ridges that diverge from the main 

 ranges of the Alps. The secondary ridges again, in their turn, 

 very frequently show in their outline a succession of prominences 

 and depressions which sometimes present a remarkable accord- 

 ance on the opposite sides of a deep valley, and are most easily 

 explained by considering them to result from the intersection of 

 transverse lines of flexure — one set of furrows being represented 

 by the existing valleys, and another by the inequalities in the 

 ridges which enclose them. Another indication of the same 

 phenomenon is apparent in the ancient lake-basins, very fre- 

 quently filled up, which recur in succession as we ascend through 

 so many valleys in the Alps. As already remarked, these lake- 

 basins were formerly larger and deeper, being almost invariably 

 separated by narrow defiles cut through barriers of rock which 

 once enclosed them. 



The formation of several of the greater lakes of Switzerland, 

 which have been called lakes of erosion, may be shown to be the 

 natural consequence of the continued action of the causes here 

 pointed out. It will be obvious that whenever forces adequate 

 to cause flexure act upon a mountain district in a direction dif- 

 ferent from that which has produced the pre-existing undulations 

 of the surface, they will leave in the new ridges which they origi- 

 nate distinct evidence of their action, and, generally speaking, 

 of the period at which they operated. But when the direction 

 coincides with that of forces previously impressed upon the sur- 

 face, the whole effect of the renewed action in the same direc- 

 tion will be to increase the existing inequalities, raising the 

 ridges, and deepening the valleys, without leaving any indica- 

 tion of the period at which the action was resumed, or whether 

 it had ever been interrupted. The great ridges and depressions 

 which have determined the main features of the Alps, which in 



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