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 structures, will be placed at equal distances along the whole line. , Six of them are now complete, and seven in progress. They are built of marble, or a light colored stone, from 14 to 20 feet in in the form of a height, rising up 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.