10 PROCEEDINGS OF SPRINGFIELD MEETING. 



The canyon of the Deerfield in western Massachusetts or of the Kanawha river in 

 West Virginia is a more manifest illustration of the principles of uniformitarianism 

 than the uplifted peneplain in which it is incised; but when the meaning of the 

 peneplain is fully realized it will come to be regarded as a much more important 

 witness than the gorge to the long continued action of every-day processes. The 

 gorge may well be subpcenaed first, but the case will not be fully proved until the 

 wide valley and the peneplain are called in to give their remarkable confirmatory 

 testimony. 



It is only within about twenty years that the second group of considerations has 

 been seriously discussed. Earlier writings show few, if any, traces of them. For 

 example, in Major Powell's explanation of the canyon of Green river through the 

 Uinta mountains, antecedent and subsequent rivers are considered, but no mention 

 is made of the possible occurrence of subsequent rivers self developed l)y headwater 

 erosion along the strike of weak strata. Hence the argument for the antecedent 

 origin of Green river deserves reexamination with the action of subsequent rivers 

 in mind. Again, in various attempts to explain the courses of the Susquehanna 

 and other Appalachian rivers, several authors of twenty or more years ago omitted 

 all consideration of adjustments of streams to structures by processes of migration 

 of divides, because these processes were not then understood. Today such an omis- 

 sion would be held as invalidating all ensuing conclusions. 



The newer discussions of the origin and arrangement of valleys must, therefore, 

 attempt to give due attention to both of the groups of considerations indicated 

 above. Postulating the essential princij)les of uniformitarianism, the life of a stream 

 should be followed from the time when it first gathers on a new land surface through 

 all following time down to the present if we would fully understand the meaning 

 of its position and its behavior. Its active channel-cutting after a time of elevation ; 

 the wasting of its valley slopes during a time of still-standing; the search thus un- 

 dertaken for weak rock structures, along which sul)sequent streams are develo})ed 

 by headwater erosion ; the continual subdivision of drainage areas and the occa- 

 sional diversion of neighboring streams by the growth of subsequent branches ; the 

 adjustment of streams to structures thus accomplished ; the meandering of mature, 

 low-grade streams and the wandering of old streams more or less from previously 

 acquired adjustments; the renewal of down-cutting when elevation occurs again; 

 the more thorough adjustment of streams to structures in a second cycle of erosion 

 than is possible in a first cycle; the powerful influence of tilting or deformation on 

 the shifting of divides ; the disturl)ing influences of climatic changes, either toward 

 aridity, humidity or glaciation — these are the more important processes and condi- 

 tions that nnist be discussed if a river course is to be seriously investigated. Little 

 wonder that the problem becomes too complex for complete solution in regions of 

 disorderly structure and long existence as dry land. 



In regions of no great age and moderate structural complications the exi)lanation 

 and therewith the appreciation of river courses may be accom})lished with fair suc- 

 cess. The most perfect example that I have found for illustrating the problem is 

 in the neighborhood of Chalons-sur-Marne, in northeastern France, where the sub- 

 sequent branches of the Marne and the Aube have diverted certain neighboring 

 consequent streams in the most systematic and symmetric manner. The story is 

 too long for narration here, but it may be found by those who care for details in a 

 forthcoming number of the National Geographic Magazine, in an article entitled 

 " The Seine, the Meuse and the Moselle." Hardly less satisfactory and much more 



