Art. VII ScHEFFEi,, Origin of Spring Vailcy Gorge. 159 



can be neither of pre-, inter-, nor post-glacial origin, but must be 

 of late glacial development. 



( )ne stej) of the ])roof that .'^])ring" \ <'ille\' is not of pre-glacial 

 origin has already been given in connectinn with the discussion 

 of the Old X'alley, but the most striking evidence against such a 

 theory is found along the course i»f Spring X'alley itself. Its 

 rock walls rise almost per])en(licular. Above them the banks 

 reach still higher, particidarly on the eastern side, over a gentle 

 debris-laden slope. The etl'ect is such that viewing the east wall 

 of the Old \ alley, as in b"ig. 'I, a citntinuous even slo])e almost 

 concealing .Spring \ alley (between the ])()ints A' and A) is ob- 

 served. Such a continuitv of sIojjc could not obtain if the stream 

 were of pre-glacial origin for if. as stated above, such a stream 

 were once formed it would soon cut through its western bank at 

 some point and drain into the major stream. 



Only abnormal conditions, as might operate during a glacial 

 epoch, could originate such a course. The divergence of the 

 united stream from debris into a rock channel on the valley wall, • 

 when the course could far more readily be continued under normal 

 conditions through drift to the axis of the major valley, can not be 

 consistently explained on any other hypothesis. 



The steep rock walls of Spring X'alley are evidence of newness. 

 The gentler slopes above them, debris-covered, indicating a well 

 eroded surface sloping to the axis of the old valley, contrast 

 sharply with these but slightl\- weathered almost vertical rock 

 walls. The slope of the stream bed is also an indication of com- 

 parative newness. The fall through Spring \"alley alone, a dis- 

 tance less than one-third of a mile, is o5 feet. 



The most striking proof of the late origin of Spring Valley is 

 found in its tributaries. It is obvious from the description of this 

 vallev already given that all secondary drainage nnist be received 

 from the eastern side. This tributary drainage is represented 

 bv the stream S, b"ig. 1. in the lower part of its course, and by 

 the two streams, which for reasons to be explained later may be 

 regarded as one, marked .S', Fig. 1 and big. .'5, in the upper part 

 of its course. 



The first of these tributaries, a tiny stream draining a small 

 area, occupies a short valley showing every evidence of maturity. 



