The Croton Aqueduct commenced about six miles above the mouth of the Croton river, where a dam has been constructed to elevate the water of the river forty feet to the level of the head of the aqueduct, or 166 feet above mean tide. The course of the aqueduct passes along the valley of the Croton to near its mouth, and thence passes into the valley of the Hudson. At eight miles from the Croton Dam it reaches the village of Sing Sing, and continues south through the villages of Tarrytown, Dobbs' Ferry, Hastings and Yonkers.

At the latter place it leaves the bank of the Hudson, crosses the valleys of Saw-mill river and Tibbits' brook; thence along the side of the ridge that bounds the southerly side of Tibbits' brook valley, to within three and a half miles of the Harlem river, where the grounds of the Hudson fall away so much as to require the aqueduct to occupy the summit of the country lying between the Hudson and East rivers.

This formation of country continues to, and is terminated by the Harlem river, at the point where the aqueduct intersects it; which is one mile north-westerly from Macomb's Dam.

The length of the aqueduct, from the Croton Dam to Harlem river, is 32.88 miles, for which distance it is an uninterrupted conduit of hydraulic stone and brick masonry. The high ground that bounds the northerly stone and brick masonry. The high ground that bounds the northerly side of the Harlem river valley, is very near the level of the aqueduct at that place; and the width of the valley at the aqueduct level is about 1450 feet, or a little over one-quarter of a mile; over which a bridge is constructed at an elevation of 114 feet above the level of high tide in the Harlem river, on which iron pipes are laid to convey the water across the valley.

The shore on the southerly side of the river is a bold, precipitous rock, rising at an angle of about thirty degrees, to a height of 220 feet, or about 100 feet above the level of the bottom of the aqueduct.

After crossing this valley, the aqueduct of masonry is resumed, and continued 2.015 miles, to the termination of the high ground on the north side of Manhattan valley.

This valley is 0.792 miles wide at the level of the aqueduct; below which it descends 102 feet. The conduit of masonry here gives place to iron pipes, which descend into the bottom of the valley, and rise again to the proper level on the opposite side; from which point the masonry conduit is again resumed, and crossing the Asylum ridge, and Clendinning valley, is continued 2.173 miles, to the receiving reservoir at York hill.

This reservoir is bounded by Eighty-sixth street on the north, Seventy-ninth street on the south, Seventh avenue on the west, and Sixth avenue on the east. It is 1,826 feet long and 836 feet wide on the outside angle of the embankment; containing an area of thirty-five acres, divided into two divisions, and is (a little over) five miles from the City Hall. From the receiving reservoir, a double line of iron pipes, three feet in diameter, is laid down in Eightieth street and Fifth avenue, to convey the water 2,176 miles to the distributing reservoir at Murray hill. The location of this reservoir is on the Fifth avenue, between Fortieth and Forty-second streets, and is three miles from the city hall; it is 420 feet square on the cornice of the exterior wall, and contains an area of 4.05 acres, divided into two equal divisions, and has an average elevation of 44.5 feet above the level of the streets around it.

The length of the aqueduct from the Croton Dam to the distributing reservoir is 40.562 miles__to wit:

Masonry conduit in Westchester county....32.800
Masonry conduit on New York Island........  4.187
                                                                   ________
Total length.....................................37.067

Receiving reservoir from end of aqueduct to south-eastern
effluent gate-house............................0.172
Distributing reservoir...........................0.080
Iron pipes on bridge over Harlem valley.....0.275
Iron pipes across Manhattan valley..........0.792
Iron pipes between reservoirs................2.176
                                                                 _________
                                                                   40.562

It is proper to add to the above, the length of the Croton reservoir, which has been formed by the erection of the Croton Dam and other work necessary to obtain the water at a suitable level on the Croton river, as without this dam and reservoir, the aqueduct would have required an extension of five miles to reach the proper level on the river; which is now attained by means of the dam. The entire length, therefore, from the point on the Croton which has the requisite elevation, to the distributing reservoir, is 45,562 miles. The large mains running from the distributing reservoir through the central part of the city, would add about four miles, making the total length of the main conduit nearly fifty miles.

A large proportion of the open cutting, and nearly the whole tunnel cutting, has been through rock. More than 400,000 cubic yards of rock have been excavated.

There are on the line sixteen tunnels, varying in length from 160 to 1,263 feet, making an aggregate length of 6,841 feet. The height of the ridges above the grade level at the tunnels, ranges from twenty-five to seventy-five feet.