GEOLOGY OF THE NEW YORK CITY AQUEDUCT l8l 



condition some portions of the drill cores being literally crushed to 

 bits. 



In one hole, no. ii, near the phyllite-limestone contact, a soft, 

 sandy condition was encountered at a depth of 133 feet, permitting 

 the drill rods to be pushed down without boring at all, 60 feet 

 ahead of the casing. This, however, is not believed to indicate any 

 very extensive weakness. It is ]3robably connected with the bedding 

 planes or joints rather than with general decay or faulting. Four 

 or five inches of solution and disintegration along bedding planes 

 would account for all that has been proven. The fact that the rods 

 could be shoved down 60 feet while the corresponding outer casing 

 could be shoved down only half as far seems to support this view\ 



Summary 



If a tunnel were made across this valley there would be approxi- 

 mately 1 100 feet of it in Hudson River slate (phyllite), 3250 feet 

 in W'appinger limestone. 600 feet in Poughquag quartzite, and the 

 rest in the gneisses. 



Some weak rock- is certain to be found, especially in the vicinity 

 of station 367^50 and 345 -00 to 350-00. At both places increased 

 water inflow would be encountered with almost exhaustless supply 

 from the sands that lie on tlie rock floor above. 



At about this stage in the exploration the Board of Water Supply 

 decided to abandon the rock tunnel plan. The conditions found 

 were considered by them too questionable. Steel pipe construction 

 is to be substituted. As a result it is not likely that much more 

 detail will be added to the structure of this very complex valley. 



