﻿GEOLOGY OF THE NEW YORK CITY AQUEDUCT 



251 



writer after studying all available data, good reason to believe that 

 the river leaves this belt when it bends to the eastward and that it 

 is in this part a displaced stream. In that case the East river could 

 be flowing upon a floor of gneiss of a most substantial sort. 



Explorations are now complete on a line that crosses the river 

 from Clinton street, Manhattan, to Bridge street, Brooklyn. All 

 borings have found good sound rock at moderate depth and all are 

 comparatively shallow holes. Their positions and depths and rock 

 types are tabulated below. 



No. of 

 bori, g 



Distances in feet 



fr m Manhattan 



pier head l.ne 



Approximate 



interval in 



feet 



Elevation of 



rock floor 



below mean 



sea level in 



f.et 



Type of rock 



Formation 



9 

 21 



53 

 3 2 

 5o 

 34 

 4i 

 39 

 67 



o 



225 



35o 



525 



695 



860 



960 



1 070 



Brooklyn side 



near bulkhead 



225 

 125 

 i75 

 170 



165 

 100 

 1 10 



48 



65 

 72 



7i 

 76 



74 

 81 

 67 



75 



Granodiorite 



Fordham 



Banded 



gneiss 



The rock floor is thus very uniform as to contour across the East 

 river at this point. No water course yet explored about Manhattan 

 island has shown so simple conditions including as it does sound 

 rock and shallow channel. The rock varies a good deal but is pre- 

 vailingly a coarse grained granodiorite. In places it is very gar- 

 netiferous and at others is banded or micaceous, but all belong to> 

 the Fordham formation as a general formational unit. 



Borings in the East river made by the Public Service Commission 

 both above and below this point found an occasional deep hole with 

 excessive decay to more than a hundred feet without securing sound 

 core. At this crossing the deepest point in the channel to sound 

 rock floor is 81 feet. 



It is certain from these results and from others in adjacent 

 ground that the East river does not occupy in this part of its course 

 the original stream channel. It has been displaced (evicted) by 

 glacial encroachment and has never been able to reoccupy the lost 

 course, Therefore, instead of the river following a belt of lime- 



