GEOLOGY OF THE NEW YORK CITY AQUEDUCT 151 



ferently from the present stream except on a steeper gradient, but 

 in all probability the headwater supplies between this stream and 

 the Moodna have been somewhar shifted. It is possible that some 

 former Moodna drainage area is now tributary to the Wallkill. 

 But tliese changes were wholly glacial in origin and the extent of 

 such shift is indeterminate at present. 



It is a notable fact that a large proportion of the work of ex- 

 ploration in this valley was done successfully by the wash rig. 



The extensive lot of data was gathered without much delay or 

 difficulty. This is because of the nature and origin of the drift 

 cover. A considerable proportion of the drift mantle especially 

 in central and deeper portion of the valley is modified assorted 

 sands, gravels and silts or muds. In part they represent deposits 

 in standing water laid down at a time when the lower (north) end 

 of the valley was obstructed by ice and while waste was poured 

 into the valley from neighboring ice fields. It is impossible to 

 reconstruct the beds of these materials with any degree of accuracy. 

 But it is at least certain that lens or wedgdike layers of differ- 

 ent quality of material were penetrated, indicating oscillation and 

 overlapping of deposition conditions, boulder beds and till being 

 interlocked with assorted sands and gravels. But there is appar- 

 ently no evidence of ice deposits of greatly differing age. The 

 accompanying profile and cross section is a representation of ma- 

 terials on the Liberty ville line based upon identifications made by 

 the inspector of the Board of Water Supply of the Wallkill Divi- 

 sion under Mr L. C. Brink, division engineer. 



