There were five completed at our last report, of 1195 feet in length, which shows an increase of two tunnels completed, of 873 feet in length. There are besides the above, nine tunnels in the progress of completion, that have been excavated in the aggregate, 2133 feet, making the total of tunnelling up to the 25th of December, 4201 feet, alnd of masonry on the aqueduct, within the tunnels, 2476 feet, being an increase, during the last six months, of 1964 feet in length. 4th. Foundation and Protection Wall The foundation wall now laid, amounts

CROTON AQ.UEDUCT. 175

to 115,210 cubic yards, and the protection wall to 114,384, making a total of 229,594 cubic yards of dry wall, which shows an increase, during the last six months, of 63,344 cubic yards of wall.

5th. Ventilators and Waste Weirs, There are 24 of these necessary structures now finished complete. A large portion of them are intended as ventilators to discharge the superabundant air collected in the aqueduct, and a few of them are fitted for waste weirs, for discharging the water from the aqueduct, if at any time repairs should be required, or any other cause make it necessary. There were six complete on the first of July last, making an increase of eighteen in this description of the work. Besides the foregoing, there has been a great deal of work performed, which cannot be described with the necessary degree of accuracy and plainness to make it understood, such as earth and rock excavation, which has been performed before the grade of the aqueduct could be reached ;