248 
ANNALS NEW YORK ACADEMY OF SCIENCES 
Page 
Department of Docks and Ferries.269 
East River Front.270 
North River Front .271 
Pennsylvania, New York & Long Island R. R. Co. 272 
East River Division.272 
Miscellaneous and Scattered Borings.277 
Astoria Light and Power Co.277 
Governors Island.278 
Plunger Elevator Holes on Manhattan .... 279 
Brooklyn Wells and other Drill Borings.280 
Deep Well of the N. Y. Quinine & Chemical Co.280 
East River and the Bay.280 
Recent Exploratory Borings of the N. Y. City Board of Water Supply 280 
Summary.281 
Areal Map and Geologic Cross section.282 
General Features of Local Geology 
A considerable portion of Manhattan Island is so heavily covered with 
drift that the underlying rock formations, as to type and structures, cannot 
be seen. This cover is especially prominent in the southern portion of the 
island. The northern portion, on the contrary, has many ridges of outcrops 
so distributed that the structural relations are quite definitely settled. Be¬ 
cause of the southerly strike of these formations, it is quite certain that they 
continue beneath the drift to the southern extremity of the island at a depth 
of from zero to 150 feet below the surface. But the available maps repre¬ 
senting the areal distribution of these formations are somewhat in error for 
certain portions of the covered area. 
The observations upon which the writer’s conclusions are based are 
chiefly drill-borings, tunnels and deep foundations that together constitute 
a considerable mass of information, some of which was not formerly accessi¬ 
ble. These data are tabulated and conveniently arranged for reference and 
comparison in the latter part of this pap.er in such a way as is thought to be 
useful for future exploration and investigation. 
Formations 
A preliminary statement, however, may be necessary as to the identity 
and characteristics of the chief formations to be considered. Of these there 
are only three of large importance: the Fordham Gneisses at the bottom; 
the Inwood Limestone overlying, and the Manhattan Schist, the topmost 
