22i5 NEW YORK STATE MUSEUM 



Harlem river, where we already have the experience of the last 

 aqueduct (the Xew Croton aqueduct; as a guide, and a very few 

 other spots. 



General conclusions 



Line I is the shortest possible defensible line. Its chief objec- 

 tionable feature is a rather long stretch, 6600 feet of limestone, 

 from 135th street to Central Park, upon the quality of which there 

 are no data. It crosses the Harlem river fault probably in gneiss. 

 But it crosses the extension of the ^vlanhattanville fault in lime- 

 stone. 



Lines F. G and H are almost equally defensible. Line G is 

 longest, but is in some respects — especially in following the ridge 

 crests — one of the best possible locations. 



It should be appreciated that many other matters, such as 

 municipal works already completed or projected, or matters of 

 engineering practice, are likely to make it necessarv* to modify any 

 line proposed, and that the hnal line is more likely to be a com- 

 promise, considering all interests. 



A graphic representation of the comparative merits of the pro- 

 posed lines is given in plate ^S- '^^^^ i^ strictly a geologic study. 

 The lines are properly placed on an outline map of the cit\- corre- 

 sponding exactly to those drawn on the geologic map, plate ^2. 

 The geologic formations that each would cut are represented on 

 longitudinal sections which follow each line, and the attitude and 

 structure of each formation are indicated. 



Revised lines 

 Subsequently two revised lines based upon the preceding studies 

 were examined to determine preference. Later one of these, or a 

 slight modification of it, was adopted as the one to be explored. 

 It was soon determined on the same reasoning as was applied to 

 the first group of lines that the most westerly line — the line keep- 

 ing as much as possible within the gneiss and schist ridges — 

 would be the most likely to give satisfactory conditions. By this 

 method of selection the unknown or untested and doubtful ground 

 was reduced to its lowest limits. It was found that nearly all of 

 the very weak spots could be located by inspection in the northern 

 portion of the line, but south of 59th street the question is de- 

 cidedly more difficult because of the heavy drift cover. Xo rock 

 outcrops occur south of 30th street, and one is reduced to the 

 evidence of deep borings. 



