2l6 NEW YORK STATE MUSEUM 



city map from Hill View reservoir to Brooklyn by three different 

 routes. So far as the topography and city development and other 

 engineering considerations could be forseen either route could be 

 used. Studies of all kinds were expected to indicate which would be 

 the most favorable and whether or not it might be advisable to shift 

 even the best one to still more favorable ground. These are shown 

 on the accompanying map which also covers the local geology of 

 the immediate vicinity of the lines [see pi. 32]. 



General questions 



When the problem of the practicability of a rock tunnel for 

 distribution conduits was first studied, several general questions 

 v/ere raised which indicate the lines of investigation followed. 



1 What is the character of the rock along the projected conduit 

 lines shown at the depths required for such tunnels? 



2 Will the rock at moderate depths be such as to permit success- 

 ful and economical construction of tunnels to be used under the 

 hydraulic pressure due to Hill View reservoir? 



3 Does the character of rock in the vicinity of the lines vary 

 sufficiently to materially affect the cost of a tunnel if the lines be 

 shifted approximately 1000 feet either way from those shown on 

 the original map as trial lines? 



4 Are the suggested locations of conduit lines adapted from a 

 geological viewpoint to the construction of pressure tunnel con- 

 duits, and, if not, what changes in these lines would be advisable? 



5 Is the thickness of rock covering sufficient at all points to 

 obviate trouble from open seams and disturbed surface rock? 



6 What borings and other field investigations should be under- 

 taken to determine the practicability of construction of pressure 

 tunnels along the lines suggested? 



In line with this series of questions a thorough geological investi- 

 gation was begun, the chief conclusions of which are given below. 



Geological formations 



There are six local formations of sufficient permanence and in- 

 dividuality of character and of sufficient areal importance to be 

 treated as units in this study. These are described in some detail 

 in part i, but for convenience are briefly listed as follows: 



I Glacial and postglacial deposits of boulders, clay and sand, with 

 silt beneath the rivers. 



