256 
ANNALS NEW YORK ACADEMY OF SCIENCES 
It is not overlooked of course that the irregular covering of drift probably 
is the most important factor in modifying the courses of many minor streams. 
This is true for the East River, also, in its lower portion. It is a displaced 
stream in part,— shoved southward out of its original course, which doubt¬ 
less was a more direct one parallel to the formations. In the submergence 
following the withdrawal of the Glacial ice a channel was established wholly 
on the drift and more than usually free from structural control. This is 
the present East River course from Blackwell’s Island southward. 
Explorations now in Progress and Their Bearing 
The conclusions reached in this paper were the outgrowth of a careful 
and detailed study of local conditions for the New York City Board of 
Additional Water Supply. The immediate importance of such modification 
of interpretation of Manhattan geology lies in the fact that it is considered 
advisable to bring the new Catskill water supply down through the city in 
a tunnel deep enough in bed rock to insure its permanence and safety. The 
changes and conditions of bed rock are therefore of very practical importance, 
and explorations in accord with the interpretations contained in the preced¬ 
ing chapter have now been in progress for several months. Points that 
were considered most critical were selected first with the idea of at once 
proving or disproving the new views of geologic structure. 
It is too early to draw sweeping conclusions or to give details, but enough 
has been established by the half-dozen holes already drilled to prove beyond 
question that in general the new interpretation of areal and structural 
distribution and relations is correct. Inwood Limestone was found in the 
first hole located to explore for it. The Fordham Gneisses were also found 
as indicated. No doubt much more detail and accuracy of boundary lines 
can be given at the conclusion of this new work. (See borings tabulated as 
Nos. 300-314). 
Configuration of the Rock Floor 
A series of observations on borings in progress and occasional well 
preserved boring materials from earlier work lead one to the conclusion 
that the rock floor of New York is very imperfectly represented in any 
attempt yet made. The reasons for this imperfection are many, but chiefly 
they are the misleading information of drill records and the almost total 
lack of discrimination between different types of loose material by drill men. 
In most cases it has been assumed by drillers that everything above the 
