6th Avenue on the east. It is 1826 "feet long and 836 feet wide on the outside angle of the embankment; containing an area of 35 acres, divided into two divisions, and is (a little over) 5 miles from the City Hall. From the receiving reservoir, a double line of iron pipes three feet in diameter, are laid down in 80th street and 5th Avenue, to convey the water 2..176 miles to the distributing reservoir at Murray Hill. The location of this reservoir is on the 5th Avenue, between 40th and 42d streets, and is three miles from the City Hall ; it is 420 feet square on the cornice of the exterior wall, CROTON ACIUEDUCT. 203 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 aqueduct from the Croton dam to the distributing reservoir is 40.562 miles — to wit : Masonry conduit in Westchester county - 32.880' Do. do. 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 Do. do. across Manhattan valley - - 0.792 Do. do. 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 distrbuting 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. DESCRIPTION OF THE COUNTRY THROUGH WHICH THE AQ.UEDUCT IS LOCATED. The soil, earth, and rock, of the country from the banks of the Croton to the city of New York, is of one general character. The line cuts a small section of marble of infe- rior quality, about two miles below the Croton dam. In running through the State farm at Sing Sing, it passes a few hundred feet (mostly by a tunnel) in a marble of pretty fair quality for building ; and again at Dobbs' Ferry and at Hastings it lightly cuts a similar rock ; at the latter place marble has been got out to some extent for market. No more marble was discovered by constructing the aqueduct until it reached Harlem river, where in excavating two of the coffer dams to obtain foundation for the piers, marble rock was found in the bed of the river. This is supposed to be a continuation of the stratum that appears in Harlem valley at the Kingsbridge road, near the Hudson river. With these limited exceptions, the prevailing rock of this district is gneiss, of great variety in quality. In many places it affords excellent building stone for ordinary purposes, and to some extent good blocks of hewn stone have been obtained. A very large proportion, however, of this rock is totally unfit for building purposes. The surface soil is generally a sandy loam, containing a very small proportion of argillaceous earth. Below the surface soil, gravel, sand, boulders, or detached rock, have in most cases been found, and also hard pan to a considerable extent. A large proportion of the open cutting, and nearly the whole tunnel cutting, ha.* been through rock. More than 400,000 cubic yards of rock have been excavated. 204 MEMOIR OF THE The general formation of the country is extremely irregular, and unfavorable for the economical construction of such a work. Commencing at the Croton dam, on a level 40 feet above the river, which descends from this point to tide-water, at the average rate of 25 feet to the mile, the grade of the aque- duct was compelled to encounter great irregularities of surface. Very little regular table- land could could be found for its location. While the main ridge of high land, that lay on the left of the line in Westchester county, controlled the general location, numerous spurs of ridges, of various forms and extent, bounded by deep ravines, rendered it im- possible to avoid deep cutting and frequent tunnelling, through ridges, and heavy rilling in the valleys ; leaving a very limited proportion of the line in favorable cutting. On the island of New York, with