CHAPTER III 



GEOLOGICAL CONDITIONS AFFECTING THE HUDSON 

 RIVER CROSSING 



General statement 



This is essentially a study of the geologic features and condi- 

 tions shown by exploration to have an important influence upon 

 the choice of river crossing for the aqueduct. In the beginning it 

 was possible to consider that any point between Poughkeepsie and 

 New York might furnish a crossing. The early preliminary in- 

 vestigations showed that it would be desirable to cross either above 

 or within the Highlands and subsequent exploratory work throws 

 light on different possible locations in these regions. Fourteen dif- 

 erent lines were tested by wash borings. Later some of these were 

 tested by diamond drill. As data accumulated it was possible to 

 eliminate many of the trial lines and the more detailed and critical 

 studies became confined to a few important possible crossings. 



In making a comparison of them as to geological environment it 

 is evident that they fall into two distinct groups^ [see fig. 15]. 

 One, that may be designated the "New Hamburg" group is rep- 

 resented by the '" Peggs point/' " New Hamburg," and " Dan- 

 skammer " Hues and is characterized by a series of much folded, 

 faulted and crushed sedimentary rocks, chiefly slates, limestones 

 and quartzites. The other, that may be called the Highlands group, 

 is represented by the '' Storm King," " Little Stony point," and the 

 "Arden point " lines and is characterized by crystalline metamor- 

 phic and igneous rock of a much older series. 



A judgment as to the most desirable crossing involves the selec- 

 tion of one of these groups chiefly upon general geologic features, 

 and finally a selection of a particular line upon minor differences of 

 materials or structure. 



In the first place it seems necessary to consider, for each group, 



1 There have been other suggestions for crossing the Hudson river, 

 farther upstream and farther down than these — one being at New York 

 city — but none have had sufficient claim to attention to encourage much 

 detailed work or so careful consideration as those here discussed. 



A shift of position of the Hudson river crossing involved a correspond- 

 ing shift of a large section of the northern aqueduct line. The first choice 

 of location occasioned a shift southward of all that portion between 

 Ashokan reservoir and the Hudson. 



[97] 



