436 J. D. Dana—On Southern Westchester County 
limestone, while numbers 8, 4, 5, 6, 10, 
11, 12 are built on piles which do not reach 
to rock, In the case of piers 10, 11, 12, the 
stone foundations, as I have learned from 
the same authority, go down thirty feet 
below high water, and the piles fifty feet 
farther. The lower ends of these piles are 
consequently eighty feet below high water 
level and yet do not reach the bottom of 
the river channel. The depth of the 
excavation, which is thus proved to exist 
there, makes it extremely probable that 
the material excavated to such a dept 
Fa 
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are 
i \ ingly probable that it extends to the bend 
Kas at 155th Street; and, since the valley con- 
e =P\ linues southward in the same line along 
Pua 
Ps 
27 IM 
garden plots, either side of the avenue, It 
is very probable that the limestone also 
continues.* These low lands or flats ex- 
tend quite to Central Park, or 110th 
“ {ae mars 
T 
AME $s 
e/a whether the limestone also extends to the 
Hsp 8 Park is among the doubtful points which 
Gas only boring or excavation can now settle. 
= ne} B. Schist east of this Eastern (or Harlem 
le ¢& Eg River) limestone band. — Me 
ASE g Comb’s Bridge, along 7th Avenue, there 
HC & ae are ledges of micaceous gneiss which are 
Hts 2 F continued to 135th Street; the beds are 
KC Y Se = nearly vertical, the dip being 70° to 80) 
HY 32 5 to the eastward to 90°, and the strike 
rp as varies little from N. 28° E. The beds 
Sectional view of the Croton Aqueduct (or High) Bridge crossing the Harlem River between Westchester County and New York Island. 
directly north of McComb’s Bridge are 
* Respecting this upper part of 8th Avenue, Dr. Gale says: “The valley 
through whee 8th Avense passes is throughont its course a perfect level and 
but a few feet above the level of Harlem River.” 
