GEOLOGY OF THE NEW YORK CITY AQUEDUCT 235 



be given to this point since the condition of these fauhs is not fully 

 known. 



5 If, as may well happen, the present East river is displaced^ from 

 its old channel by glacial drift, so that it is essentially an evicted 

 stream, there may not be as pronounced a channel or as weak ground 

 to cross at such points as at those where the old channel is still oc- 

 cupied. In such case both of these lines are favorable. 



6 On the other hand, the crossing of line P is almost a mile 

 nearer to the great Hudson gorges, to which doubtless this portion 

 of the preglacial East river was tributary, and consequently its bed 

 rock channel, if it is the real preglacial channel, may be expected 

 to be deeper and the accompanying disintegration (so far as it may 

 be controlled by this factor) may be expected to reach lower than at 

 points in similar surroundings farther up stream. It is impossible 

 to say how much weight should be given to this objection. It does 

 not seem to be of sufficient importance to fully offset the favorable 

 features indicated in items i, 2, 3 and 4. 



On the basis of these studies line P (the southerly one) near 

 Manhattan bridge was chosen as the site of preliminary exploration 

 promising the most favorable results. Later this was shifted a short 

 distance without introducing any new conditions. 



1 Exploratory borings indicate that such has been the history of the river. 



