GEOLOGY OF THE NEW YORK CITY AQUEDUCT 



2=; I 



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 co.uld 

 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. 









Elevation of 







No. of 

 bori, g 



Distnces ii feet 



Approximate 



rock floor 







fr m Manhattan 



interval in 



below mean 



Type cf rock 



Formation 



pier head l.ne 



feet 



sea level in 













f.et 







9 









-48 



Granodiorite 



Fordham 



21 



225 



225 



-65 





" 



53 



350 



125 



— 72 







32 



525 



175 



— 71 







50 



^95 



170 



-76 







34 



860 



165 



— 74 



« 



u 



41 



960 



100 



— 81 



" 



u 



39 



I 070 



no 



-67 



" 



u 



67 



Brooklyn side 

 near bulkhead 





-75 



Banded 



gneiss 



u 



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

 river at this point. Xo 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 

 cere. 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- 



