142 



Bulletin of Laboratories of Denison University. [Vol. XIII 



Gap A is now the valley of a slight stream which rises in Perry 

 Township. This creek is rock bound at a point just southwest of 

 Boston Corners where the ice so abutted the nose of a spur that 

 the drainage was forced across it thus cutting a channel which 

 has held the stream since. From this point southward almost to 

 its intersection with the highway, the creek skirts the conglomer- 

 ate clift's of the Black Hand. Throughout most of its course, 

 however, the washings from the ice front have obscured the lower 

 contours of the valley represented by A. 



The next gap, B, is not so pronounced in its rock topography 

 as the two cases just described. The hills immediately east and 

 west (Fig. 6) are rock; the area intervening, and to the north, 

 is buried with drift. Even with a moderate thickness of drift — 

 a well at Boston Corners shows 50 feet and no rock — it is obvious 

 that the rock rim of the divide dropping into the filled valley north 

 is very much lower than the row of rock hills which the ice- 

 margin skirts eastward. B then marks a gap of the same kind 

 but not of the same degree as the others. 



FUj. 6. Looking? a little north of o«st from the top of the west wall of gap 

 A. The curve in (he traction line is in front of the southern end of sap li. The 

 stream of A now enters B through a rocl{ channel at foot of the wooded slope 

 in right foreground ; the camera stands about -00 feet above this channel, hence 

 the picture does not show the former course of this stream. 



