24 
ROCK FLOOR OF GREATER NEW YORK. 
[BULL. 270. 
number, however, have been obtained from the valuable " Memoranda 
of Elevations/'" which is in use among engineers. 
It is well understood that this list does not include the records of 
all borings which have been made on the island, and it is therefore 
hoped that others will supplement them so far as possible. 
Fig. 3.— Sketch map of Manhattan Island showing location of special 
longitudinal and tranverse sections. 
It will be well to consider the form of the rock pedestal of the island 
as it appears in important sections, which, as the result of recent 
a Brown, M.B., Memoranda of Elevations, New York City (unofficial), 1883, pp. 17. r >. (New York. 
49-")i Park place. ) 
