572 MARIUS R. CAMPBELL 



unrecognizable. These movements may produce a complete 

 transformation of the drainage features of a land area by causing 

 a portion of it to be depressed below drainage level ; or they 

 may cause the revival, or rejuvenation of the streams by lifting 

 the land above its previous position. In any case the modifica- 

 tions arising from such movements will fall under the first class, 

 or those due to the natural course of events in a normal cycle of 

 development. 



Crustal movements of the second, or local class affect but a 

 limited area. They consist of uplifts or depressions which 

 reach a maximum along an axial line, grading off to the undis- 

 turbed strata at no great distance on either side. The local 

 movements which have occurred in the past have not generally 

 been intense enough to cause a perceptible dip of the rocks, but 

 they have elevated the surface into broad ridges, or depressed 

 it into shallow troughs. 



The effects of these local movements upon the drainage 

 must have been very different from the general movements. 

 They would cause no general revival, but would affect the 

 streams locally, and consequently their effect in producing rear- 

 rangement must have been very much more potent. The prin- 

 cipal object of this paper is to study the effect of these local 

 movements upon the streams ; to endeavor to establish the crite- 

 ria by which the changes due to this influence may be recog- 

 nized ; and lastly to apply these criteria to a continental area, 

 and by their assistance endeavor to read the history of the region 

 in question. 



(3) IDEAL CASES ILLUSTRATING THE EFFECT OF LOCAL EARTH 



MOVEMENTS. 



In studying this subject in the field, the observer is frequently 

 confused by local conditions of geologic structure and alterna- 

 tion of hard and soft strata, which apparently overshadow the 

 more subtle influence of crustal warpings ; although the latter 

 may, in a general way, be the dominating force which has 

 shaped the drainage systems. In a theoretical consideration of 



