GEOLOGY OF THE NEW YORK CITY AQUEDUCT 269 



2 East side of A'illa avenue north of Bedford Park boulevard. 



3 East of the Concourse between 198th and 199th streets. 



4 South side of 196th street both east and west of the Concourse. 

 One of these occurrences was known to the geologists of the 



United States Geological Survey [New York City, Folio No. 83] but 

 it was regarded by them as an infold of the Inwood. An examina- 

 tion of all four occurrences will convince one that they are not 

 in foldings. In at least two cases the structure accompanying the 

 beds is actually anticlinal instead of synclinal. 



These occurrences in the vicinity of Jero iie Park reservoir are 

 essentially the same as those disclosed by the borings of the Lower 

 East Side. In spite of its thick drift cover — 50 to 200 feet — 

 there are more limestone interbeds known there than in any other 

 area of similar size in the region. It is entirely possible that a 

 thorough exploration in certain other belts might reveal an equally 

 elaborate development elsewhere. 



The substantiation of interbedded limestones as a prominent 

 element in certain facies of the gneiss series and their association 

 with typical silicious gneiss layers with transitional relation em- 

 phasizes still more the strictly sedimentary origin of at least soma 

 portions of the Fordham series. Other observations lead to the 

 conclusion that they are the oldest members of the series and that 

 the igneous associates, of which there are many, are all younger 

 intrusives. 



One of these later intrusives is the Ravenswood granodiorite 

 which cuts into the eastern margin of the Lower East Side, forms 

 the floor of the present East river channel at the point of aqueduct 

 crossing and continues as far as explorations have been carried into 

 Brooklyn. 



Structural detail of Low^er East Side 



What the detailed structure of the Lower East Side is, it is im- 

 possible to say at the present stage of exploratory development. Its 

 general features of structure are fairly clear. The Manhattan schist, 

 which is the universal floor rock of the central and western part? 

 of Manhattan island, extends only a short distance east of the 

 Bowery. The Inwood limestone comes to the surface of the floor 

 at Christie and Forsyth streets. An anticlinal ridge of gneiss comes 

 up at Eldridge and Allen streets. Then a syncline of Inwood 

 limestone is pinched into the next three or four blocks and from 



