150 Bulletin of Laboritories of Dejiison Utiiversity. Vol. XIII] 



its surface features, we infer that this most distal position of the 

 ice was maintained for some time (Fig. 3). i\nother rather pro- 

 longed halt ' in the retreat is apparent at and immediately west 

 of the Swigert well. The depth of clay found in this well, and in 

 the well of Mr. Felix Claypool at Boston Corners is also evidence 

 of unmodified drift. Kettle holes, many of them not yet filled by 

 vegetation, are common. The topography indicates another halt 

 of the ice across the valley near Boston Corners ; the fourth halt 

 going west is in the section crossed by the road northward from 

 the Brick Plant ; the last halt concerned in this problem is marked 

 by the slope just east of the Rocky Fork (Fig. 8), a slope which 

 has been considerably deformed by later stream terracing. 



The delta-like reaches of the Hanover Dam, it should be 

 noted, lie in rock-walled segments of this old valley. The appa- 

 rent exception in the position of gap, B, is not real, for the follow- 

 ing reason : when the ice retreated from the northern end of this 

 gap it left a ridge of drift ; this was the retreat that followed 

 halt 2. This ridge of drift fitting against the rock hills both north- 

 west and northeast of the letter B, on Fig. 3, had the effect of a 

 rock enclosure, exerting the same control as the rock slope east 

 of Hanover. The withdrawal of the ice from position 2 to posi- 

 tion 3 was gradual, leaving in its path a marked morainic topo- 

 graphy. The retreat between halts 3 and -i was more rapid ( Fig. 

 10) ; while a much longer period of time was used, and a corre- 

 spondingly greater drift accumulation was formed (Fig. 9), by 

 the ice before making the last stand, halt 5. 



It appears then that when the ice-tongue fronted at position 3 

 there extended eastward as far as position 2 a fairly static reach 

 of water ; this was an evanescent condition, bu't was of sul^cient 

 duration to partially level-up the hummocky surfaces with an as- 

 sorted deposit varying in thickness. 



We note the same combination of conditions again when the ice 

 stood at position 5. But here the work was probably on a larger 

 scale, because the normal ice-front drainage was greatly aug- 

 mented by the accession of the waters of the Rocky Fork which 

 was carrying the run-oif of a valley dependency extending east- 

 ward from Wilkins Run (p. 133). Gap A for some time conducted 



• These halts are indicated on the topographic map, Fig. .3, by 1, 2, etc. 



