CHAPTER XIX 

 SPECIAL EXPLORATION ZONES 



Exploration by borings^ and other methods have been made at all 

 questionable or uncertain points along the line. As was expected 

 in the beginning five places have required elaborate exploration and 

 some exceptional conditions have been proven. The original 

 geological investigation based upon surface study as outlined in the 

 foregoing pages served to locate these spots accurately. 



These places or zones, now either finished or sufficiently well 

 known to permit accurate statement of geologic conditions, are as 

 follows : 



1 The Harlem river crossing at 167th street, where the aqueduct 

 will cross from a ridge of Fordham gneiss beneath the Harlem river, 

 where the whole thickness of Inwood limestone will be cut, to the 

 ridge of Manhattan schist above the Speedway on Manhattan island. 



2 The Manhattanville cross valley, a low pass crossing the island 

 at about 125th street. The part explored extends from St Nicholas 

 to Morningside Parks and crosses a zone with very low rock floor 

 in the Manhattan schist. 



3 From Morningside to Central Parks. The line crosses the 

 strike of the formations at this point and cuts a longitudinal fault 

 and anticlinal fold which tends to bring the Inwood limestone 

 within surface influence. 



1 Exploratory work has been in direct charge of Mr T. C. Atwood, division 

 engineer, who has followed all stages of it almost from the beginning. In 

 the later exploratory work an immense amount of detail and a very com- 

 plex lot of data has accumulated requiring constantly the services of a man 

 with some special geological training. Mr John R. Healey, formerly in the 

 testing laboratory, was transferred to this special field. He is probably 

 more familiar with the multitude of details resulting from boring operations 

 along the conduit line than any one else. Except for the care and good 

 judgment used by these men in preserving data, and the wisdom of the 

 men who planned the line and methods of work before them, much valu- 

 able geologic data would have been lost. Notwithstanding the best efforts 

 of the consulting geologist some really critical points escape unless some one 

 constantly on the ground is directly interested in them as a part of the 

 regular responsibility. 



237 



