40 W. M. DAVIS 



graded streams permits the flaring sides of their valleys to consume 

 the greater part of the upheaved surface and thus to produce sharp 

 ridges (p. 267), essentially as in a following stage of Penck's ideal 

 cycle; but some small unconsumed remnants of the initial surface 

 may still survive at this time. A fully matured stage is then 

 described as follows : 



A long-continued upheaval has now brought about a still greater altitude 

 and the deep attack of erosion has produced a strong relief. As long as the 

 upheaval is active, even the large rivers must have a torrential flow; they will 

 cut down deeper and deeper, but will be still unable to develop flood plains. 

 So deep have they already cut and so well are the valley sides opened upwards 

 that all the higher parts of the upheaved initial surface have now been consumed. 

 The characteristic features of a maturely dissected mountain range — still 

 under the postulate of almost homogeneous structure — are: .... sharp peaks 

 and ridges with numerous little rock outcrops bat with the slopes generally 

 covered with creeping detritus. The most notable of these features is the 

 systematic arrangement of the slopes, so that all detrital and water streams 

 from every peak and ridge descend along well prepared converging lines into 

 their valleys [pp. 274, 275]. 



A following paragraph makes mention of the similar summit alti- 

 tudes usually observed in maturely dissected mountains, and refers 

 to Penck's principle of a limiting upper level of denudation as 

 its cause. 



Here a question of nomenclature arises. According to Penck's 

 latest scheme, sharp-crested mountains are described in his 

 '^Gipfelflur" essay by a paraphrase above quoted; it is added that 

 their youthfulness prevents their being characterized, following 

 Davis, as mature. But this correction, like the others already 

 noted, appHes quite as much to Penck's own earher terminology 

 of the erosion cycle as to mine. Sharp-crested mountains are not 

 youthful according to his definition of that stage of erosion in the 

 Scobel Handhuch: young mountains are there said clearly to 

 exhibit remnants of the upheaved surface, which may be large 

 enough to deserve the name of plateau (Sc. 147; also Figs. 83,1; 

 84,1). Hence now to call sharp-crested mountains youthful is 

 quite as much a departure from his own earher scheme as from 

 mine. Let such a departure be made freely if it seems an improve- 

 ment on previous pronouncements ; but it does not seem appropriate 



