EROSION AND THE SUMMIT LEVEL OF THE ALPS 19 



rapidly much increased in volume at the time of capture, may for 

 a time be overfit in relation to its valley pattern. It is beheved 

 that underiit rivers may also result from climatic change, as well 

 as from a reduction of stream volume (during unchanged»climate) 

 by loss of surface water to underflow in the flood-plain deposits of 

 mature valleys, according to what I have called Lehmann's princi- 

 ple, after its discoverer/ Streams that, by reason of uplift, have 

 lengthened their courses across an emerged sea floor, were called 

 extended by Tarr; if extended streams, formerly separate, are led 

 to join in a single trunk, I have called them engrafted; if the 

 branches of a trunk river are separated by the submergence of their 

 main valley, they may be called betrunked or dismembered. 



It is manifest that many of these terms may be used in any 

 rational method of physiographic description, but they are peculiarly 

 helpful in the explanatory method based on the scheme of the 

 erosion cycle because the features that they designate are so closely 

 related to one or another of its successive stages. Thus, while 

 consequent streams are defined by the initial slopes of a land surface, 

 and are as a result established at the beginning of a cycle, subse- 

 quent streams are not well developed till a mature stage is 

 reached, and obsequent and resequent streams are of later develop- 

 ment than subsequents. Similarly, grade is a condition that 

 characterizes the stages of maturity and old age; river captures, 

 especially the captures of consequent headwaters by growing 

 subsequent streams, occur chiefly in the stage of maturity. The 

 adjustment of streams and ridges to belts of weak and resistant 

 structures is also a characteristic of the mature and later stages; 

 and so on. 



Gradual development of the cycle scheme. — A correspondent has 

 called my attention to an aphorism of Hegel's, to the effect that a 

 new truth has a short period of victory between an earlier time when 

 it is opposed as a heresy and a later time when it is passed by as a 

 commonplace. Such is truly the case with the general principle 

 that subaerial degradation may in time reduce any mountainous 

 highland to a nearly featureless lowland, on which the scheme of 



'"Meandering Valleys and Underfit Rivers," Ann. Assoc. Amer. Geogrs., Vol. Ill 

 (1914), pp. 3-28. 



