HOBB8] COVERED PORTION OF THE ROCK EASEMENT. 23 
rock surface of the island, the significance of rock contours with] 
Massachusetts-Connecticut area having demonstrated the value of . 
studies. In the area on and immediately surrounding the island obse 
vations from nearly 1,500 borings or excavations to rock have been 
collected through the courtesy of many corporations and private indi- 
viduals. For these valuable data the writer has been placed under 
obligations to many city and Government officials, engineers, archi- 
tects, artesian-well borers, and others. In addition to those mentioned 
on page 21 as supplying the greater number of data bearing on the 
nature and depth of the rock bed of river channels, there should be 
mentioned Mr. Russell Bleicker, secretary of the department of docks; 
Mr. George Livingston, commissioner, and Mr. Joseph O. B. Web- 
ster, engineer of street borings, of the department of public works; 
Mr. Watson G. Clark and Mr. Peter Elbert Nostrand, city surveyors; 
Mr. Robert Maynicke, and Messrs. Clinton & Russell, architects; 
Mr. Palmer Campbell, general manager of the Hoboken Land and 
Improvement Company; Mr. M. S. Starrett, engineer of the Inter- 
urban Street Railway Company; Mr. Daniel E. Moran, of the Founda- 
tion and Construction Company; Mr. William D. H. Washington, 
Washington Building; Mr. A. C. Veatch, of the Hydrographic Divi- 
sion, United States Geological Survey, and Mr. C. B. J. Snyder, 
architect, of the department of education. Among the contractors 
for artesian wells who have supplied valuable information are Mr. Isaac 
H. Ford, 104 Fulton street; Messrs. Stothoff Brothers, Flemington, 
N. J., and Mr. Harry E. Estes, of the New York and New Jersey Well 
Company. Brewing companies of the cit}^ have freely supplied infor- 
mation concerning the driven or bored wells upon their premises. 
' Voluminous data from these sources have been included in Part II, 
pp. 30 to 93. The greater number apply particularly to the " down- 
town " portion of Manhattan, south of the gneiss upland area, and to 
the area of the Harlem flats north of 110th street. The data from the 
downtown area have been entered on the map forming PL I, after 
having been corrected so as to refer to the United States datum plane 
of mean tide at Sandy Hook. a 
The observations from the Harlem area have been similarly entered on 
the map forming PL II. The grades of street intersections from which 
the depths below datum have been computed, were obtained in part 
directly from the official records, through the courtesy of Mr. George 
Livingston, commissioner, and Mr. Joseph O. B. Webster, engineer 
of street openings, of the department of public works. The larger 
aThis datum plane is the one adopted by the U. S. Coast and Geodetic Survey and the Pennsyl 
vania Railroad Company. It is located 2.49 feet below the datum of mean high water at New York 
City, adopted by the New York department of public works and the Rapid Transit Comn 
is 2.25 feet above the datum plane of mean low water at New York City, wiiich has been i 
the New York dock department. The Pennsylvania, New York and Long Island Railroad 
has adopted the datum of mean high water, and to avoid the use of signs has fixed this elevation as 
300 feet. 
