124 REGINALD A. DALY 



level. Local notches or cols may be gnawed in the ridge, but all 

 the summits must be roughly accordant, though, of course, not uni- 

 form, in altitude. Other things being equal, the more mature the 

 dissection, the more perfect the summit-level accordance; but the 

 principle may be applied to alpine ranges. In those ranges the 

 actual imperfect degree of accordance may often match the imper- 

 fectly matured state of dissection. 



GENERAL CONCLUSION AND SUMMARY 



The form of the preceding discussion has been analytical, but its 

 main point has been to emphasize the synthetic nature of the process 

 of mountain sculpture. Seven different conditions of erosion work 

 together to produce accordance of summit levels in an ideal alpine 

 range undergoing its first cycle of physiographic development. 

 Isostatic adjustment and simultaneous, differential degradation of 

 rising blocks tend to bring about rough accordance of summit levels 

 in the range as "originally" formed. Later differential erosion and 

 consequent further isostatic adjustment, the influence of metamor- 

 phism and intrusion, the sculpture due to high-level glaciation, the 

 normal existence of a high-level tree-line, and, finally, the compound 

 process of river-spacing and slope gradation — all these may combine 

 their effects and render more perfect the accordance of levels inherited 

 from the early, growing period of the range. 



In an actual range, as distinguished from the ideal range, all seven 

 of these conditions may not be present; the efficiency of those that 

 are present make the special problem of that special range. 



The composite explanation of accordance must always face the 

 alternative explanation of the peneplain theory. The latter theory 

 involves two physiographic cycles in the history of the range, and 

 attributes summit-level accordance to inheritance from the initial, 

 upwarped peneplain surface of the second, present cycle. Several of 

 the chief conditions of erosion on which the composite explanation 

 is based, tend, of course, to preserve the accordance of levels inherited 

 from the peneplain. 



The strength of each of the two explanations is so great that a 

 decision as to which is true for a given alpine range may need nice 

 discrimination. Nevertheless, the profound differences between the 



