The Pompton River has a drainage area above Mountain View of 420 square miles. It is formed near the head of the basin by the confluence of the Pequanac from the northwest, the Wanaque from the north, and the Ramapo from the northeast. * * * The entire flow from this watershed may be stored by building a dam across the gap at Mountain View and converting Pompton Plains into a great lake covering an area of 21 square miles. The elevation of the river at the gap is 168 feet. The slopes in the basin being gentle up to an elevation of 220 feet and abrupt beyond it, it will be advisable to take this as the minimum or low-water level of our reservoir. It is generally estimated that 25 per cent of the volume of the mean annual rain on a given catchment is sufficient reservoir capacity to fully utilize the flood flows. We have long series of observations of rainfall at three points, which may be taken to fairly represent the Passaic catchment. At Newark the mean annual rainfall is 46.2 inches, at Paterson, 50 inches, and at Lake Hopatcong, 42. The last being on the Highlands, like most of our watersheds, is perhaps the safest to use. Now, 25 per cent of 42.5 inches, 10.62 inches, which, on 420 square miles, give a volume of 10,362,000,000 cubic feet, the necessary capacity of reservoir. By raising our reservoir to 240 feet when full we secure a capacity of 10,493,000,000 cubic feet, or ample to utilize the heaviest floods of the watershed. This gives a beautiful sheet of water 21.1 square miles in area, with bold, rocky shores, and a depth at dam of 72 feet. We secure the above capacity by uncovering but 22 per cent of the reservoir bottom; and, as we shall presently see, we shall rarely need more than half this storage, and probably not oftener than once in ten years will we expose over 10 per cent of the area. By building side dams to keep certain flats always flowed this may be reduced to 5 per cent; and this area will be pretty evenly distributed around 36 miles of uninhabited shore line, leaving the reservoir open to no valid sanitary objections. On the contrary, by relieving the remainder of the Passaic Basin of the flood waters of the Pompton, which now flow large areas of flat land during wet seasons, the sanitary condition of the valley would be much improved. In constructing this reservoir Mr. Vermeule stated that the following work would be necessary: The removal of the Delaware, Lackawanna and Western Railroad from the basin by changing the alignment for 6 miles. It may be done without increase of length or detriment to the alignment. Three and one-fourth miles of the Morris Canal must be rebuilt. No engineering difficulties are involved. Of the New York and Greenwood Lake Railway, 9 miles would have to be rebuilt.