234 NEW YORK STATE MUSEUM 



Such evidence as has any bearing upon this question has already 

 been used in formulating the interpretation of geologic structure 

 given in the foregoing sections of this report. If the succession and 

 boundaries of formations as outlined are reasonably close to the 

 actual conditions, it would appear that line P (the southerly one 

 just above ^Manhattan bridge) has some advantage over line Q 

 (near Williamsburg bridge). The chief elements in this advantage 

 are as follows : 



1 It would appear that line P might lie wholly within the Ford- 

 ham gneiss in the East river section, while line O may cross two 

 contacts. 



2 From the evidence of borings made in the East river at 14th 

 street^ it appears probable that a belt of schist similar to ^Manhattan 

 schist in quality (whether accompanied by limestone or not there is 

 no direct evidence) lies in the river channel toward the east side and 

 in all probability extends southward in the middle of the river at 

 Williamsburg bridge. This would be cut by line O. The uncertain- 

 ties of this association are of sufficient importance to throw the bal- 

 ance of present choice toward line P. 



3 If the theory that the East river course is due chiefly to zones 

 of weakness following fractures or faults is true, their possible 

 comparative condition as they cut through different formations must 

 be taken into account. There is little doubt on this point but that, 

 in zones of similar original disturbance, those in the Fordham 

 gneiss have suffered less extensively from disintegration than those 

 cutting either the limestone or schist. Therefore, obscure as it may 

 be. the preference is again in favor of Hne P. 



4 If, furthermore, the course of the river is due to cross faulting 

 or any similar or related displacements or movements, an inspection 

 of the structural map indicates that the controlling zone followed 

 by the river as it crosses line Q must have a general strike north- 

 west, while the corresponding zone that crosses line P strikes east. 

 Of these two types (directions) of fault zones, so far as they may 

 be judged to have influence in the adjacent area, there is no doubt 

 but that the northwest type (the set that has a northwest strike) 

 is both the more common and the more important. If this general 

 tendency is also true here, then on this account also line P may be 

 considered slightly more favored. In reality not much weight can 



1 These borings were made by the Public Service Commission in explora- 

 tions for subways. 



