258 
ANNALS NEW YORK ACADEMY OF SCIENCES 
before the present ideas of the differentiation of formations on Manhattan 
or their structure were known, and some were in the care of engineers and 
others who made no special claim to a knowledge of rock classification. 
Besides, the purposes for which they were usually taken seldom made it 
necessary to know anything more than that bed-rock had been reached and 
that it was substantial enough for foundations. The depth to rock was 
almost the only information needed in most cases. It is, therefore, somewhat 
surprising, all things considered, that these materials have been so intelli¬ 
gently noted and so carefully preserved. Some of them are from twenty 
to thirty years old, but the greater number have been gathered within the 
past fifteen years. In many cases no one has made examination of them 
since their original individual purpose was fulfilled. 
No other enterprise' has found it so necessary to follow up all these 
sources of bed-rock information. Therefore this is the first time any one 
has examined all of these data in an attempt to classify them and use the 
information in interpreting the rock structure and formational geology of 
the areas covered hopelessly beneath the heavy drift cover of the southern 
part of the city. The task has required more work than is likely to be 
warranted soon again. Believing also that the information may be occa¬ 
sionally serviceable in tabulated form, as well as in interpretations reduced 
to geologic maps, the following sets of abbreviated notes are offered for 
preservation in the records of the Academy. 
I am well aware that these notes leave much to be desired. It is often 
absolutely impossible to classify a bit of rock from a drill core or identify it 
with any particular local formation. This is because of the similarity of 
certain varieties of two of these formations, — the Manhattan Schist and the 
Fordham Gneiss. Occasionally in a boring only a few small chips represent 
all that is recovered or saved. An extensive core or a group of specimens 
almost always makes it possible to determine the identity with satisfaction. 
I have taken some care to indicate whether the classification given is reason¬ 
ably certain, or simply a preference for one of the possible formations, or 
whether it is entirely indeterminate. I am sure no one will more fully 
appreciate the difficulty of making a rigid classification of such cores than 
the men who know these formations best. 
The tabulation includes location, depth to rock, depth uniformly cor¬ 
rected to U. S. Coast and Geodetic Survey datum, which is mean sea level 
at Sandy Hook, penetration of the rock, present classification as to relation¬ 
ship to local formations and variety or quality of special features. It is not 
generally possible to give data of value as to percentage of core recovery, 
for the reason that it is not possible to know whether or not the original core 
was all saved. 
