68 NEW YORK STATE MUSEUM 



rejuvenate the streams and permit them to begin the sculpturing 

 of the land in a new cycle of erosion is perfectly clear. As soon 

 as the elevation and warping of the continental border made its 

 influence felt in the increased activity and efficiency of the streams 

 (rejuvenation) they began transporting the alluvium of their flood 

 plains and to sink their courses through this loose material to bed 

 rock. The final result of long continued denudation under these 

 conditions in early Tertiary time was the removal of the loose 

 mantle and the beginning of attack on bed rock (superimposed 

 drainage). The streams formerly flowing on alluvium that had 

 now cut down to rock found themselves superimposed upon a 

 rock structure not at all consistent with their former courses. 

 With the progress of erosion on this rock floor all these differ- 

 ences of structure, such as the difterences in hardness of beds, 

 the trend of the folds, the strike of the faults, the igneous masses, 

 etc., were discovered and the streams began to adjust their courses 

 to them. Valleys were carved out where belts of softer rock 

 occur, ridges were left as residuary remnants where belts of harder 

 rock exist, and the surface (relief) took on some of the char- 

 acter of present day lines. That is, the principal mountain ranges 

 of that time were the same as those of today in position and 

 trend; but they had not so great apparent hight because the in- 

 tervening valleys had not yet been cut so deep. The principal 

 escarpments of that time were due to the same structural lines 

 as those of today, only they have shifted somewhat along with 

 the general retreat of all prominences by the forces of weathering 

 and erosion. 



In the co'urse of this work of sculpturing and the shifting of 

 valleys and divides and escarpments and barriers into constantly 

 greater and greater conformity with rock structure, it came about 

 by and by that practically all of the smaller and tributary streams 

 had so completely adjusted themselves to their geologic environ- 

 ment that their valleys almost everywhere followed along the 

 softer beds (subsequent streams), the divides were chiefly of 

 harder beds, the trend of both were almost everywhere parallel to 

 the strike of the rock folds and other structures (adjusted drainage) 

 This undoubtedly involved in many cases a very radical change of 

 stream course, and in some cases an ultimate reversal of drainage 

 to such extent that tributaries were deflected inland against the 

 course of the master streams and in some cases actually flowed 

 many miles in this reversed direction before finding an accordant 

 junction (retrograde streams). At least three of the streams of 



