GEOLOGY OF THE NEW YORK CITY AQUEDUCT 253 



stone around this big bend as was formerly supposed, it follows no 

 rock floor structure at all but is in this part of its course wholly 

 superimposed. The original valley lies farther to the west cutting 

 through the midst of the Lower East Side where the more com- 

 plicated geologic structures again prevail. 



Borings at intervals of 500 feet have now been made on the 

 Brooklyn side of the East river to Gold street and Myrtle avenue. 

 So far as developed there is no other formation than the Fordham 

 and the associated granodiorite within the area covered. The rock 

 floor is remarkably uniform at an elevation of from -70 to -90 

 feet. The accompanying section shows the relations of rock floor 

 to present drift surface [fig. 40]. 



STRUCTURAL GEOLOGY OF THE LOWER EAST SIDE, 

 DELANCEY AND CLINTON STREET SECTION 



The proposed distributary conduit turns from the Bowery east- 

 ward on Delancey to Allen street, thence on Allen to Hester street, 

 thence on Hester to Clinton street and follows south on Clinton 

 to the East river. This so called Lower East Side section includes 

 one of the most complicated geologic structures in New York city. 

 The most complex portion extends from Christie street on the west 

 side to Monroe street on the east. Between these two points all of 

 the crystalline rock formations form a series of parallel beds that 

 are folded together so closely that they stand practically on edge. 



This general fact and the approximate location of the several 

 beds have been proven for some time. But the more exact structure, 

 with the depths to which the beds go before bending upward again, 

 and the distances through each one are only approximately deter- 

 mined by the exploratory borings to date. The chief uncertainties 

 arise from the fact that the beds are also faulted and the dips of 

 the fault planes are not yet determined and the amount of displace- 

 ment is unknown. The difficulty of forming a good estimate of the 

 obscure points is greatly increased by the fact that no rock of any 

 kind is to be seen at the surface. Judgment is based wholly on 

 borings. 



There are other important questions covering the zone, such as : 

 (i) depth of serious decay, (2) location and width of these decay 

 belts, (3) general physical condition of the rock at certain levels, 

 (4) length of tunnel that will cut each formation, (5) best depth 

 for safe construction. 



The accompanying geologic cross section [pi. 38] embodies an 

 opinion of the structural relations of the different formations. It is 



