GEOLOGY OF THE NEW YORK CITY AQUEDUCT 83 



I Points of exploration^ 



a Tuff crossing. This line is a half mile above Peggs point. 

 Wappinger limestone forms the east bank of the river and Hudson 

 river slates the western bank. There seems to be no abnormal 

 structural relation of the formations. All data are from wash 

 borings. The accompanying section gives the results, 



b Peggs point line. Peggs point is 2 miles north of New 

 Plamburg. At this location Wappinger limestone forms the east 

 bank and Hudson river slates the west bank of the river as in the 

 previous case. The limestone dips gently westerly while the slates 

 have a variable attitude. This is a normal relation and there is no 

 direct evidence of any great structural break. A large number of 

 wash borings have been made and five diamond drill holes were 

 driven, three of them in the river. None indicate a greater depth 

 than 223 feet, although there is a wide stretch, 1040 feet, not ex- 

 plored by the diamond drill. This space must contain the deeper 

 gorge if one exists here. From the known conditions at the 

 entrance to the Highlands, 10 miles further down stream, where 

 the channel is known to be more than 500 feet deeper, it may be 

 rather confidently asserted that a deeper inner channel does exist at 

 this point. 



c New Hamburg line. This line crosses the Hudson from 

 Cedarcliff to the village of New Plamburg. The river is narrow — 

 only 2300 feet. There are no drill borings within the river channel, 

 but there is one on each bank. Both penetrate Wappinger lime- 

 stone first and then pass into Hudson river slates beneath. How 

 much of a gorge exists here is wholly unknown except in so far as 

 may be judged from the wash boring. There are the same reasons 

 for believing that a gorge exists as those noted for the Peggs point 

 line. 



Structurally this line is probably the one of greatest complexity. 

 It is however perfectly clear that the abnormal position of the 

 slates and limestone on the east side of the river is caused by a 

 thrust fault. A similar relation of the slates and limestone on the 

 west side must be due to a like movement, but whether they are 

 separated portions of the same structural unit or of two adjacent 

 ones is not clear, although they are probably distinct 



1 All of these explorations on the Hudson river have been under the direct 

 supervision of Mr William E. Swift, division engineer, in charge of the 

 Hudson River division. 



