THE GEOGRAPHICAL CYCLE AND ITS COMPLICATIONS 591 



presentation may soon be advisedly expanded to include regions of 

 resistant rocks which are uplifted slowly and in which the first-cut 

 valleys of the larger streams are maturely open or "mature-born" from 

 the beginning; also regions of weak rocks in which, even if the uplift 

 be relatively rapid, the first-cut valleys will be "mature-born"; and in 

 which, if the uplift be slow, the first-cut valleys may be deepened so 

 little in excess of the down-wearing of the inter-valley uplands that the 

 general expression of the surface will at once be "old." Indeed, one may 

 conceive of a region that, after a first very slow uplift, is uplifted more 

 rapidly, but eventually stands still for an indefinite period; and in such 

 a case the expression of the first-developed valleys would be "old" ; 

 then as the rate of uplift increased, the "old" valleys would be first 

 incised by "mature," and then by "young" valleys; and finally the 

 "young" valleys would, during the ensuing still-stand period, gradually 

 gain the appearance of "mature" and "old" valleys. Nevertheless, it does 

 not seem advisable to base the general terminology of the whole scheme 

 on so special a case, but rather to modify a generally applicable termi- 

 nology so as to adapt it to such a case and to various other cases, as need 

 arises. 



The other dissenting correspondent proposes to give up the scheme 

 of the cycle because he has found that the small headwater streams of an 

 uplifted and partly dissected peneplain occupy wide-open but shallow 

 valleys, even though the trunk rivers flow in narrow, deep, and steep- 

 sided valleys. I had myself come upon such headwater valleys during 

 an excursion in central France in the winter of 1898-99, and have pub- 

 lished an explicit account of them, as well as what seems to me a simple 

 and sufficient explanation of them, in my Berlin lectures of 1 908-09. 3 

 The general scheme must therefore be modified so as to recognize that, 

 even if trunk rivers incise typical "young" valleys in an ..uplifted pene- 

 plain, their little headwater branches will probably have "mature-born" 

 valleys from the beginning of the new cycle of erosion. Hence my feeling- 

 is here again : Modify the scheme to include this principle as a matter of 

 course ; but why give up all the rest of the scheme because a modification 

 is needed here! 



Climatic Changes during a Cycle of Erosion 



But besides these two correspondents there are other geographers, 

 particularly Hettner of Heidelberg and Passarge of Hamburg, who 

 reject the scheme of the cycle as essentially incorrect in omitting many 



8 Die erklarende Beschreibung der Landformen. Leipzig, 1912, See pp. 62, 259, 



