BERKEY, GEOLOGY OF SOUTHERN MANHATTAN ISLAND 253 
changes in pitch, — some due to faulting, and others due to igneous intru¬ 
sion. The abundance of these irregularities makes it doubly difficult to 
trace a formation or contact beneath the drift any great distance beyond 
actual outcrops. For this reason, in southern Manhattan, drill holes, 
foundation excavations and tunnels have great value in determining a more 
reliable distribution. It was a study of all known sources of such informa¬ 
tion that first suggested the changes in areal and structural geology of 
Manhattan that are here given. 
Areal and Structural Corrections 1 
Below Central Park there is now little evidence to be gathered at the 
surface as to areal or structural geology, but as far south as Thirtieth Street 
the bed-rock geology is pretty well known from earlier reports and from 
recent improvements that have exposed the underlying rock. All of this 
portion is mapped as Manhattan Schist, except one small area of serpentine 
at Fifty-ninth Street between Tenth and Eleventh Avenues. There is no 
reason to modify this usage in that portion of the island. A careful study 
of a great number of rock specimens from the Pennsylvania Railroad tunnel 
across Manhattan at Thirty-second Street proves beyond question that the 
bed rock is Manhattan Schist, including almost all known variations and 
accompaniments, for the whole width of the island along that line. 
Farther south the points that have furnished exact information about 
bed-rock are less numerous, and below Fourteenth Street they are confined 
to deep borings or an occasional deep excavation for foundation. Even 
these sources of information are lacking over large areas. The greater 
number of borings available are along the water front. Their character 
and distribution are such as to indicate that the west side and central portion 
of the island are underlain by Manhattan Schist. (See accompanying map 
on which these data are plotted.) 
This is true entirely to the East River at Twenty-seventh Street and as 
far eastward as Tompkins Square at Tenth Street and almost to the Man¬ 
hattan tower of Brooklyn Bridge in that vicinity. 
To the eastward of these limits, that is, to the eastward of the line pro¬ 
jected from Blackwell’s Island to the Manhattan tower of Brooklyn Bridge 
(Bridge No. 1), there is evidence of a more complicated geology. The 
borings of the East River front are decidedly variable. They are certainly 
not all Manhattan Schist. Those most unlike the Manhattan are at the 
same time most like some varieties belonging to the Fordham Gneiss, and it 
1 Based upon the data tabulated on pages 260-281. 
