640 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



' The activities of erosion do not appear to tend toward more -uniform 

 effects with greater altitude, on the contrary elevation emphasizes their 

 locally unequal intensities. Corrasion and transportation are effected by 

 falling water, whose energy for a given mass is directly as the fall, and 

 consequently increases with height of land. Corrasion and transportation 

 are very narrowly localized in activity, and hold the same relation to 

 general degradation that a circular saw does to a planer. Their intense 

 application results in deep canyons, the extreme of height and depth. 

 Disintegrating influences, whether chemical or mechanical, may act equally 

 with equal opportunity, but they are controlled by conditions of exposure. 

 Upon an uneven surface these are varied and they become more and more 

 diverse as inequalities of relief develop. The suggestion that frost and 

 thaw may with elevation gain in effectiveness more rapidly than corrasion 

 and so may limit the height to which peaks may attain in a growing range, 

 appears not to be sustained by study of mountains much higher than the 

 Cascades, nor by theoretical reasoning in regard to the work of freezing 

 water. Thus after careful consideration the writer has felt obliged to 

 abandon the hypothesis of development of a common high level among 

 mountain peaks.'* 



The reply to this argument is implied in much that has preceded in the 

 present chapter. A chief objection to it consists in the fact that under the 

 arid conditions above tree-line we have in falling water only one, and perhaps 

 not the most important, cause of erosion. Waste-streaming, wind-action, snow- 

 creep, and avalanches must also be considered. It seems clear, therefore, that 

 Willis's argument is inconclusive; it does not support the two-cycle hypothesis 

 of the Cascade range topography. 



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 of the underlying 

 ideas. f 



Professor Shaler in America and Professor Eichter in Europe have inde- 

 pendently 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, 



*B. Willie, Prof. Paper No. 19, U.S. Geol. Survey, 1903, p. 74. 



t Cf. E. S. Tarr, American Geologist, Vol. 21, 1898, p. 351 ; N.S. Shaler, Bull. Geol. 

 Soc. America, Vol. 10, 1899, p. 263; W. S. T. Smith, Bull. Department Geology, Uni- 

 versity of California, Vol. 2, 1899, p. 155; E. Richter, Zeitschrift des deutschen und 

 osterr'eichischen Alpenvereine, Vol. 30, 1899, p. 18; W. M. Davis, American Geologist, 

 Vol. 23, 1899, p. 207. 



