344 



Howard Clark 



An important feature of this drift is the extent to which it has 

 suffered weathering. Fig. 3, B. shows its irregular surface, and 

 the interlocking spurs in one of the many small valleys which 

 have been cut back into the drift. Its age is also indicated by 

 the degree to which the boulders have suffered chemical change; 

 some of the fine-textured crystalline rocks, which would be 

 expected to resist weathering more than the others, on being 

 broken, show an altered band nearly one-half inch wide. These 



Fig. 4. Cross-sections of the Rocky River valley arranged in down-stream 

 order, 1 to 3; for their location, consult fig. 1. 



facts indicate a considerable length of time since the drift was 

 deposited. Leverett maps it under Illinoian.^ 



A possible lake. The glacier standing across this south open- 

 ing valley must have produced an ice-front lake, if the drainage 

 was then flowing southward. The size of this lake would be 

 determined by the location and altitude of its overflow channel. 

 If the outlet was in segment A, the narrowest part of the valley, 



Loc. cit., p. 342. 



