RIVER TERRACES AND REVERSED DRAINAGE 6 J J 



valley side, and only by the rarest chance are destroyed in the 

 curve adjacent to the down-valley side. That these terraces are 

 preserved with a south-flowing stream, upon the north side, or 

 up-valley, would seem to indicate that there had been a north- 

 flowing stream since the drift deposition of glacial time. 



It is evident that there has been a reversal of drainage since 

 the initial development of the valley in preglacial time, but the 

 position of the terraces would indicate that they were due to the 

 postglacial meandering of a north-flowing stream, and that their 

 preservation was due to the superimposition of the stream on the 

 projecting rock spur. That there has been a second reversal 

 since the inception of the close of the glacial epoch, subsequent 

 to the drift deposition, does not seem rational. Though a post- 

 glacial uplift may have taken place, it does not appear from any 

 analogous development in the region that it was of a sufficiently 

 revolutionary character to bring about such a change. 



As both the highest level terrace plain and the lowest part of 

 the valley bottom are a homogeneous, assorted, and glacio- 

 fluviatile drift, from one end of the valley to the other, the pos- 

 sibility that the terraces are remnants of a flood plain developed 

 previously to the glacial epoch is not great. If they are the 

 result of lateral swinging by a south-flowing stream, of constant 

 volume, they should have been undercut and concentrated, or 

 else distinctly modified by its successive meanders. 



It is not essential to the solution to discuss in detail the 

 various causes of reversed drainage, whether by headwater 

 piracy, ice erosion, aggrading, or land tilting, nor the evidences 

 of the same as expressed in the Catatonk Valley; but, so far as 

 either the negative or the positive evidence of the terraces sug- 

 gests anything, it tends to strengthen the belief that neither 

 slope, load, nor volume has remained constant since the drift- 

 filling and aggrading took place. 



There is some additional evidence in the fact that the terrace 

 fronts have a vastly greater arc of curvature than is developed 

 by the swing of the present stream. 



It seems likely from the fragmentary evidences that the val- 

 ley was occupied, for a time subsequent to the withdrawal of the 



