11 miles and one-fifth. The increase in this part of the work, since our last report, is 18,418 feet, or about three and a half miles in length. 2d. SIDE WALL. — The length of side wall ready to receive the brick facing and arches, was, at our last report, 1~443 feet. It now amounts to 17,535 feet, making an increase in this description of the work, of 16,092 feet, in six months. 3d. CULVERTS. — There are 92 culverts now complete and in use, leading off the water of the several streams at which they are the conduits. Their length in the aggre- gate is 6,240 feet. The number completed at our last report was seventy-nine, and their length 5,476 feet. There is, therefore, an increase of 13 in the number of culyerts built since our last report. 4th. TUNNELS. — The number of tunnels excavated through their whole length, is jive, and in the aggregate, are 1,197 feet long. Only three were completed at our last report, of 667 feet in length, which shows an increase of two tunnels completed, 530 feet in length. There are in progress of completion, besides the above, six tunnels, which have been excavated in the aggregate, 1,809 feet, making the aggregate of tunnelling, up to the 25th of June last, 3,00(3 feet, and of masonry in the tunnefs, of 1,707 feet, being an increase since our last report, of 1,152 feet. 5th. FOUNDATION AND PROTECTION WALLS. — The foundation wall laid, is 91.980 cubic yards, and protection wall, 74,270, making a total of 166,250 cubic yards. The quantity of this description of work performed at our last report was 95,027 cubic yards, which shows an increase, for the last six months, of 71,221 cubic yards of foundation and protection wall. 6th. VENTILATORS AND WASTE WEIRS. — These necessary and ornamental struc- tures, will be placed at equal distances along the whole line. , Six of them are now com- plete, and seven in progress. They are built of marble, or a light colored stone, from 14 to 20 feet in height, rising up in the form of a pyramid, and may answer to point out to strangers, the line of the aqueduct, as well as vents, through which the collected air may discharge itself. CROTON ACIUEDUCT. 173 There is, in addition to the above, a vast amount of labor which cannot be well described, except by extending this report to an inconvenient length — such as the rock and earth excavation, the stone quarried and dressed, the vast embankments thrown up in the numerous valleys and ravines, over which the aqueduct has to pass, with the neces- sary machinery and tools prepared for carrying on the operations. Some important and expensive structures, however, which are not included in the sketch given above, ought not to be omitted, although the description must be very brief and imperfect. Take for example the following : 1st. An archway over a street, in the village of Sing Sing, of 20 feet span, and 14 feet in height. 2d. The aqueduct bridge over the Sing Sing Kill a considerable run of water, pos- sessing several mill privileges. The arch of this bridge is 88 feet span, and about 70 feet in height from the bed of the creek. The centres for turning this large arch, have been up for some time past, and thirty courses of the arch stone laid. The aqueduct proceeds from the Sing Sing tunnel, crossing both the aforesaid street and creek, from north to south. 3d. An archway over the Highland turnpike, now highway, about eleven miles below the Croton dam, of 20 feet span, and 14 feet in height. 4th. The large culvert on Mill River, requiring an arch of 25 feet span, and 170 feet in length, situated about thirteen miles below the Croton dam. The depression of the valley through which this stream passes, is 72 feet below grade, and the height of the foundation wall, including the aqueduct, reaches to 87 feet above the bed of the river. 5th. A very expensive archway, forming a carriage way under the aqueduct, at Jewell's Brook, about seventeen miles from the Croton dam, of 14 feet span, and 125 feet in length. The foundation wall at this place is 50 feet in height to grade, and 62 feet to the top filling of the aqueduct. 6th. An aqueduct bridge over the railroad at Harvey's marble quarry, of 16 feet span, and 10 feet in height. 7th. An archway over the road at Saw Mill River, of 16 feet span, and 14 feet in height. 8th. The large double culvert on Saw Mill River, with arches of 25 feet span each and 82 feet in length. The river is 42 feet below grade,