SUMMIT LEVELS AMONG ALPINE MOUNTAINS 123 



(7) The chemical solution of rock is, to be sure, probably more 

 rapid beneath the forest-cap than it is above tree-line where the 

 amount of vegetable acid is at a minimum. This cause may, how- 

 ever, be believed to do little toward counterbalancing the effect of 

 the combined causes just enumerated. Erosion in alpine mountains 

 takes place primarily by the removal of masses; in comparison, 

 molecular transfer of rock material to the low grounds has but a very 

 minor control. 



Conclusion.- — A review of the conditions of general degradation 

 shows clearly its differential character above and below tree-line. 

 Summits already reduced to the tree-line are bound henceforth to 

 be stubborn against further erosion. Summits bearing a treeless 

 zone are as clearly bound to continue wasting rapidly so as to tend 

 to approach accordance of summit levels with their tree-covered 

 neighbors. Since the glaciated zone of alpine mountains is, in gen- 

 eral, well within the treeless zone, the special degradation due to local 

 glaciers harmonizes with general erosion in the development of accord- 

 ance. 



5. Accordance through river-spacing and gradation of slopes. — A 

 fifth method for the spontaneous development of summit-level 

 accordance remains to be noted. The recent announcement and 

 discussion of this explanation make it superfluous to present here 

 more than the briefest analysis of the underlying ideas. 1 



Professor Shaler in America and Professor Richter in Europe 

 have independently shown that, as mature dissection of a region 

 under normal climatic conditions is reached, rivers of the same class 

 tend to become nearly equally spaced. In perfect maturity the 

 slopes of the interstream ridges are graded from top to bottom. This 

 gradation of the slopes draining into two adjacent, nearly parallel 

 streams flowing in the same direction, produces a comparatively 

 even longitudinal profile of the intervening ridge. The even crest 

 of the ridge must be more or less sympathetic with the profiles of 

 the streams below, and, down stream, slowly attain a lower and lower 



1 Cf. R. S. Tarr, American Geologist, Vol. XXI (1898), p. 351; N. S. Shaler, 

 Bulletin of the Geological Society 0) America, Vol. X (1899), p. 263; W. S. T. Smith, 

 Bulletin of the Department of Geology, University of Colorado, Vol. II (1899), p. 155; 

 E. Richter, Zeitschrift des deutschen und osterreichischen Alpenvereins, Vol. XXX 

 (1899), p. 18; W. M. Davis, American Geologist, Vol. XXIII (1899), p. 207. 



