carries the face over and meets the back line of the wall. The back line is carried up ver- tically, with occasional offsets. The main body of the work is laid up of rough stone ; the curved face of large and closely cut stone, with four heavy courses at the bottom dove- tailed together, the joints cut to the line of radius of curve. Above the masonry an embankment of earth is filled in, and extends to 275 feet in width on the bottom, with a slope of one to five on the up-stream face. The north end of the new weir is germinated by an abutment that rises 12 feet above it. From the toe of the masonry an apron is extended 35 feet, composed of hewn timber secured by ties, bolts, and treenails, in a very substantial manner, and filled for 16 feet from the stone work, with concrete masonry, and the remainder with loose stone, and covered with a course of 6 inch white elm plank. A second apron is partly made which is to extend 30 feet further. At 300 feet below the main dam, a second dam is in progress, which is to be 9 feet high, constructed of timber, stone and gravel, which will set the water back over the apron of the main dam, and form a pool to check the water as it falls on it. A coffer dam was constructed in the river to inclose about 120 feet of the work, from which the water was pumped by a steam engine, and a concrete foundation laid down on a very firm hard pan. The remainder of the foundation was made by sinking timber piers at suitable distances, running parallel with the dam, and filling the spaces between them with concrete masonry. In preparing the specifications for this work, the method and order of prosecuting it was particularly designed, and from which no material departure has been found necessary ; the structure is now nearly completed. The contractors, Messrs. McCullough, Black, McManus, and Hepburn, have evinced a highly commendable energy and ability in its prosecution. This dam sets the water of the river back five miles, and forms a reservoir of about four hundred acres, and has rendered it necessary to construct several new roads and bridges as a substitute for those covered by the flow, the principal of which is the So- merstown turnpike. The grounds lightly flowed on the margin, have been excavated so as to give 4 A feet for the least depth of water. From this reservoir the water flows into the bulk-head, at the upper end of the tunnel, from a level averaging 10 feet below the surface. AQUEDUCT BRIDGE AT SING SING. The Sing Sing kill,, where it crosses the line of aqueduct, runs in a deep and narrow gulf, the bottom of which is 63 feet below the grade line, or 76 feet below the top covering of the masonry. Over this gulf an aqueduct bridge has been constructed. Near the north end of the valley that spreads out from this gulf^ a road culvert, or arched viaduct has been constructed under the conduit. The principal work here is the large arch directly over the gulf. It is 88 feet span, and 33 feet rise ; the form is an oval drawn from five centres ; the abutments are commenced on GROT ON AaUEDUCT. 209 the solid rock, near the bottom of the gulf. The work is constructed of well dressed stone masonry, laid in hydraulic cement. Open hance walls are carried up over the inte- rior and above the solid spandrels, and united at the top by brick arches. The spaces between the hance walls are carried entirely across the crown of the arch, to afford as much facility as possible for any water that might leak from the conduit to pass off. The depth of arch stone at the spring line is four feet, and at the crown three feet. The para- pets and walls of the conduit are carried up with an opening of six inches between them, more effectually to guard against the effects of frost, and to carry off any water that might leak from the conduit, and prevent its being absorbed by the outer or parapet wall. The conduit over this bridge is constructed of stone and brick masonry, so arranged as to receive a lining of cast iron ; the iron being set back so as to receive a facing of brick over the bottom and sides, which is further secured by three courses of hydraulic cement plastering. It is not probable that any considerable quantity of water would have escaped, if there had been no other security than the stone and brick masonry ; but it