GEOLOGY OF THE NEW YORK CITY AQUEDUCT 225 



Details of rock conditions along these lines are as follows : 

 Line F. (Westerly) beginning at Hill View reservoir 



Feet 



7 600 Yonkers gneiss — good quality 

 15000 Fordham gneiss — good quality 

 2 000 Fordham gneiss — probably 2d grade 



1 200 Harlem river crossing — partly limestone — 3d grade 

 14800 Manhattan schist — good quality 



1600 Alanhattanville crossing — 3d grade — some limestone 



2 600 Manhattan schist — good rock — through Morningside 



Park 

 800 At south end of Morningside Park — perhaps some lime- 

 stone — 2d grade 

 1400 Manhattan schist — good — to junction 

 12000 Manhattan schist — along Central Park — good 

 20600 To East river — Manhattan schist — less known^ — (fair) 

 (2d grade) 

 6 000 To Brooklyn '' unknown "^ 



85 600 Line G 



Feet 



8 400 Yonkers gneiss — good rock 

 17 600 Fordham gneiss — good rock 



which brings it to the Harlem river where the other line (F) is 

 joined. Although the line is about 1400 feet longer, it avoids some 

 low ground (2000 feet) along the east bank of the Harlem river, 

 some of which may be in poor condition. Total length of line, 

 87,000 feet. 



Line H 



Feet 



8 400 Yonkers gneiss — good quality 

 23 800 Fordham gneiss — good quality — to Harlem river 

 I 000 Crossing Harlem river — probably fault zone in gneiss 



800 Fordham gneiss — good quality 

 I 000 Limestone — 2d grade 



I 200 Manhattan schist — good quality — to junction with the first 

 line (F) at 145th street 



From this point the line is the same as F and G. Its chief ad- 

 vantage is the great distance which it has in Fordham gneiss. 

 Total length of line, 85,600 feet. 



' Subsequent explorations made by the Board of Water Supply have elimi- 

 nated this unknown ground. See later discussion. 



