164 Bulletin of Laboratories of Denison Uniiwrsitv. Vol. xill] 



part of the rock be the most weathered, a reversal of wliat is 

 found in normal streams. Spring' X'alley gorge corresponds with 

 the latter in this respect. 



Glacial Theories. Early Glacial. — That such a gorge as that 

 of Spring \'alley might have beeti formed during early glacial 

 times would be quite in accordance with the accepted explanation 

 given later. The difference, however, is apparent. It is not 

 probable that the ice would maintain a stable position relative to 

 this channel throughout a long interval of time. There would be 

 many advances, retreats and halts. Its chance for survival during 

 such changes in tlie ice movement would be the same as for any 

 deep depression. It would be filled with debris and smoothed to 

 correspond with the adjacent topography. 



Sub-glacial Theory. — That sub-glacial streams are of frequent 

 occurrence is a fact well known to the literature. That such 

 streams frequently follow courses independent of topography is 

 equally well known. Such streams, however, are usually over- 

 laden with debris received directly from the ice. This, together 

 with the restraint of the ice-covering reduces their cutting efifi- 

 ciency, sometimes even making them so inactive that deposition 

 rather than erosion obtains. In Spring Valley an erosional ac- 

 tivity is evidenced with few parallels in known sub-glacial stream 

 courses. Further argument against this theory is similar to that 

 in the preceding paragraph. Even if formed under such condi- 

 tions as mentioned, the instability of the ice would tend to change 

 the channel, as well as to fill any channels that might be formed 

 with glacial debris. However favorable the conditions, none of 

 these channels could escape the influence of the ice-retreat. 



Late-Glacial Theory. — Wdiile it is impossible to prove without 

 question such a genesis, nevertheless in the theory of a late-glacial 

 origin of Spring \ alley it is difficult, if not impossible, to tind 

 unanswerable objections to any of its phases. 



During this period the Old X'alley can be imagined as occu- 

 pied by ice reaching out over the west, abutting against its east 

 wall an<l extending as a tongue for some distance along the 

 valley of the Raccoon, the ratio between advance and retreat at 

 this time approximating unity. Lnder such conditions the ice 

 would melt away from its up])er contact with the east wall of the 



