GEOLOGY OF THE NEW YORK CITY AQUEDUCT IO5 



It is largely an ancient stratified series much metamorphosed con- 

 taining belts of interbedded limestones, quartzites, and schists, in 

 addition to the more substantial feldspathic gneiss. The eastern 

 bank of the river bears also abundant evidence of extensive crush- 

 ing and shearing and is believed to indicate a displacement in this 

 zone. For these reasons the West Point crossing is considered an 

 unfavorable route compared to either of the others of the High- 

 lands group. 



Summary. In a comparison of the geologic features that are 

 of most importance in contrasting the possible routes for the Hud- 

 son river crossing the following points are considered of most 

 importance. 



1 The New Hamburg group of crossings involves (a) the long- 

 est tunnel, (b) the more complicated structures, (c) the greatest 

 number of known faults, crush zones, and related disturbances, 

 (d) the more variable series of rock types to be penetrated, (e) 

 the greater tendency to encounter heavy underground water circula- 

 tion, (/) the greater probable susceptibility to disturbance from 

 future earth movements, and (g) the greater number of uncer- 

 tainties of rock relations. 



2 In contrast the Highlands group admits of (a) shorter total 

 tunnel length, (b) the most profound fault lines of the district are 

 crossed either in high ground or are avoided or, because of the 

 rocks involved, promise the least possible trouble, (c) the Hudson 

 river itself can be crossed in a single formation with probability of 

 avoiding line^ of largest structural weakness confining the greatest 

 pressures and deepest tunnel work within the most uniform and 

 substantial rock of the whole region. 



There are, of course, many unknown or only partially known 

 features obscured beneath the covering of drift or lying beneath 

 the river itself ; but, however many there may be, it is not believed 

 that they can materially change the general situation. The major 

 characteristics are so well marked that any addition to those already 

 known would in all probability increase the difficulties of the New 

 Hamburg group of routes at least as much as and perhaps more 

 than those of the Highlands group. 



In view of the above facts and inferences the judgment has been 

 in favor of the Highlands group of crossings as the more defensible 

 on geologic grounds as a route for the aqueduct line. Furthermore, 

 in accord with the preferences already noted, the Storm King loca- 

 tion is regarded as the most likely to give satisfactory results. 



