262 
ANNALS NEW YORK ACADEMY OF SCIENCES 
fore, to correspond to this datum, which is also the datum of the Board of 
Water Supply. All three of the rock formations of this district are pene¬ 
trated by these holes. One is in Manhattan Schist, one is in typical Inwood 
Limestone and three are in the oldest formation, the Fordham Gneiss. 
Three others, supposed to have struck rock, seem to me not to have reached 
it, and two others penetrate decayed and disintegrated rock of $o badly 
altered character that it cannot be accurately identified. 
Serial No. 
Original 
Mark 
Location 
Depth 
to rock 
M. H. W. 
To Rock 
U. S. 
datum 
Rock 
penetra¬ 
tion 
Form¬ 
ation 
Variety and remarks 
33 
1 
Pier headline 
-6S.0' 
-65.2S' 
32.7' 
Manh. 
Mica schist typical. 
34 
2 
60' E. ditto 
Drift 
No bed-rock at -99.0'. 
35 
24 
330' E. ditto 
-93.0' 
-90.28' 
7.0' 
Inw’d. 
Coarse dolomitic cry¬ 
stalline limestone. 
(Pieces were found at about 75-77' first and still further down. The material is disinte¬ 
grated micaceous variety of Inwood Limestone.) 
36 
3 
585' E. ditto 
-10S.0' 
? 
Arkose sand. May be 
disintegrated Fordham 
-101, -108. No solid 
bed-rock at -10S'. 
37 
4 
900' E. ditto 
-37.4' 
-34.68' 
52.2' 
Ford. 
Granitic gneiss banded 
and very micaceous. 
38 
4A 
1150' E. ditto 
-60.2' 
-57.48' 
29.8' 
Granitic gneiss more 
micaceous than usual. 
39 
5 
1380' E. ditto 
-107.28'? 
Drift 
Probably no rock at 
-107.28'. 
40 
6 
1775' E. ditto 
-87.58' 
? 
Micaceous green mud, 
probably decomposed 
micaceous limestone (In¬ 
wood). No solid ledge. 
41 
7 
2190' E. near pier 
-S7.6S'? 
Drift 
Probably no ledge at 
headline 
-87.68'. 
42 
8 
L. I. R. R. Co.’s 
-45.9' 
-43.18' 
24.1' 
Ford. 
Granodiorite of mottled 
pier 
garnetiferous type, mas¬ 
sive and streaked. 
Department of Bridges 
The materials obtained by drill borings in investigations for sites of 
piers and anchorages for bridges across the East River have been examined. 
These materials are housed at different places as indicated below in each 
case. In general, the evidence of bridge borings is especially satisfactory 
and definite because of the fact that they are always in groups. This gives 
opportunity to compare several from a single area and to correct or cor- 
