BERKEY, GEOLOGY OF SOUTHERN MANHATTAN ISLAND 269 
b) Brooklyn side. 
Serial No. 
Original 
mark 
Location 
Depth 
to rock 
M. H. W. 
To Rock 
U. S. 
datum 
Rock 
penetra¬ 
tion 
Form¬ 
ation 
Variety and remarks 
119 
F 
Dock St. 
-97.5' 
-95.78' 
7.4' 
Ford. 
Granodiorite gneiss, gar- 
netiferous. 
120 
G 
At angle in pier- 
headline N. Y. 
Dock Co. 
-85.25' 
-S3.53' 
4.35' 
Granitic gneiss, banded, 
crumpled. 
121 
I 
N. end of B'klyn 
Bridge pier 
-84.7' 
-82.98' 
10.12' 
“ ? 
Mica gneiss. 
122 
J 
Between I and 
Water St. 
-77.3' 
-75.58' 
4.28' 
Granitic gneiss, striped 
black and white. 
Department of Docks and Ferries 
The borings represented in the following list were made by the Depart¬ 
ment of Docks and Ferries at a large number of pier sites along both the 
Hudson and East Rivers. Many of them were made twenty to thirty years 
ago, and they probably constitute the oldest group of such data in the city. 
The material of the borings represents the muds, sands and gravels of the 
overburden, as well as the bed-rock. They are all fully labeled, boxed and 
housed at the yard of the Department of Docks and Ferries, at foot of 
Twenty-fourth Street and East River. The samples of rocks are all in the 
form of fragments (not cores) secured from chopping into bed-rock. In 
most cases they represent but slight penetration of the rock floor, seldom 
more than two or three feet. In some cases, especially where but a small 
sample is recovered from an uncommon variety of rock, or from a some¬ 
what decayed bed, it is impossible to determine the formation name. It 
is more difficult than where solid cores are obtained. In the following 
tabulation the variety of rock and formational relation as now used are 
given wherever possible. The original names such as “Granite” and 
“Syenitic Granite” used chiefly in the sense of crystalline bed-rock are 
avoided. 
The datum used by the Dock Department is Mean Low Water. On 
Nov. 22, 1898, however, the datum was raised 0.2-F. The Board of Water- 
Supply datum (Mean Sea Level at Sandy Hook according to the U. S. 
Coast and Geodetic Survey) is 2.09 ft. higher than the present Dock Depart¬ 
ment datum (M. L. W.), and is 2.33 ft. higher than the M. L. W. of the 
Dock Department as used prior to 1S98. As all of the borings tabulated 
here are older than that date, the latter correction is used in reducing to 
U. S. datum. 
