GEOLOGY OF THE NEW YORK CITY AQUEDUCT 189 



Summary 



The lowest bed rock is about sea level. 



This pressure tunnel will cut only jNIanhattan schist. 



All rock is good ground for such work, except in certain narrow 

 zones where it is crushed. 



The extent of such broken ground is not closely delimited, but 

 occurs at intervals for a distance of 700 feet. 



The amount of underground circulation is judged to be moderate 

 at -100 feet. 



The tunnel should be located deep enough to take advantage of 

 the improved rock conditions shown at about —100 feet. There 

 seems to be no marked improvement below -100 feet as deep as 

 the drills have s^one. 



