14 



NEW YORK STATE MUSEUM 



been diverted to the south along the course of Riley brook and so 

 escaped to the sea or Lake Champlain. Such notches are normal 

 features in many eskers where no streams occur. The marked 

 crease on either side of the esker is quite characteristic and sug- 

 gests that, as has been noted of some eskers in the upper Missis- 

 sippi valley, the glacial stream occupied the bed of an older valley. 

 The esker ends rather abruptly south of Ingraham and affords 

 no evidence of having been the path of a stream connecting 

 directly with a frontal outwash plain or esker fan. 



I have examined the major portion of the length of the esker 

 in the search for shore lines. Dr Gilbert first noted slight traces 

 of a beach near Ingraham. Both the esker and the adjacent 

 swampy depressions unfilled by marine or lake deposits show that 

 this belt, which lies from 3 to 5 miles distant from the beaches 

 at the base of the adjacent high ground on the west, received very 

 little sediment during the sojourn of the sea over this field and 

 thus is in sharp contrast with the deposits of marine sands and 

 clays which occur along the lake shore. Below Ingraham the base 

 of the esker is contoured by the 140 foot line ; near its northern 

 end by the 200 foot line. The ridge itself seldom if ever rises 

 more than 40 feet above the adjacent low ground. 



Deltas contemporaneous with ice fronts 



Two classes of deltas of gravel and sand may arise along the 

 margin of an ice sheet. First, those produced by the outwash of 

 sediment from the ice by the discharge of its drainage; and, 

 second, those deposits which are laid down by streams flowing 

 toward the ice margin from the open country which it has perhaps 

 just vacated. Deltas of this latter class may form terraces banked 

 up against the ice margin, or, where temporary lakes form along 

 that margin, the delta may take on its typical form and structure 

 and not be distinguishable in itself from a delta built in any 

 ordinary nonglacial body of water. All the principal streams in 

 this area exhibit occasional deltas of gravel and sand, the upper 

 ones of which are probably to be regarded as contemporaneous 

 with the retreating ice sheet. 



