136 INTRODUCTION. 
the villages of Sing-Sing, Tarrytown, Dobb's ferry and Yonkers, where, leaving 
the Hudson and crossing the valley of Sawmill river and Tibbitts brook, it gains 
the summit between the Hudson and East rivers, and continues on that summit 
to the Harlem river, a distance of 32°880 miles of continuous masonry. tron 
pipes are then laid 1450 feet, on an arched bridge, across the valley of the 
Harlem river, at an elevation of 114 feet above high tide. After crossing the 
valley, the aqueduct of masonry is resumed and continued two miles to the Man- 
hattan valley, which is passed with iron pipes, descending 102 feet to the bottom 
of the valley, and continued rising again to its opposite side, the distance across 
the valley being 0°792 mile. The masonry conduit is again resumed, and cross- 
ing the Asylum ridge and the Clendinning valley, is continued 2°173 miles to the 
receiving reservoir at Yorkville. This basin is 1826 feet long and 836 feet 
wide, and including its embankments, contains an area of thirty-five acres divided 
into two parts; from thence iron pipes are laid beneath the surface of streets 
2°176 miles, to the distributing reservoir at Murray hill, three miles from the 
City Hall. 
This reservoir is 420 feet square, and covers four acres. It is divided 
into two equal parts, and has an average elevation of 44°05 feet above the 
level of the adjacent streets. The length of the aqueduct, including the iron 
pipes and reservoir, from the Croton dam to the receiving reservoir, is 45°562 
miles; and including the elevated surface of the Croton river, and the large 
mains conducting the water from the distributing reservoir through the central 
parts of the city, the entire length is 50 miles, of which the masonry conduit 
constitutes 37°067 miles. The rocks through which the line of the aqueduct 
passes are two marble quarries in Westchester, and for the residue of the route 
gneiss of many varieties. A large portion of the open cutting, and nearly 
all the tunnel cutting, have been made through rocks, more than 400,000 feet 
of which have been excavated. The formation of the ground is very irre- 
gular. There are on the line sixteen tunnels, varying in length from 160 feet to 
1263 feet, and being in aggregate length 6841 feet. The height of the ridges 
