a sufficient head to force it across the Harlem river, and to deliver it at the distributing reservoir in the city, at an elevation equal to the supply of the loftiest edifices. The engineer contents himself with having established the practicability of deliver- ing the Croton into the city at a comparatively reasonable cost, and leaves it to be deter- mined by future and more minute examination, what route shall be adopted. Of the quality of the Croton water, Mr. Douglas gives this account : " The supplies of the Croton are derived almost exclusively from the elevated regions of the ' Highlands' in Westchester and Putnam counties, being furnished by the pure springs, which so remarkably characterise the granitic formation of that region. The ponds and lakes delineated on the map, and spoken of in a former part of this re- 30 MEMOIR OF THE port, are among the number of these springs ; many of them 3 or 400 acres in extent, and one as large as a thousand acres. All these ponds are surrounded by clear upland shores, without any intermixture of marsh ; and the surrounding country, cultivated as it is generally, in grazing farms, presents an aspect of more than ordinary cleanness. The water, as might be expected under such circumstances, is perfectly soft and clear, much superior in the former respect to the waters of our western lakes, and fully equal in the latter. The Croton, fed by such springs, could scarcely be otherwise than pure, and the fact of its purity was strongly verified by the experience of the party in every stage of the water during the season. Specimens were taken up both in the high and low state of the river, and have been analysed by Mr. Chilton, and the results obtained fully corroborate these statements. It appears from his report annexed, that the quantity of saline matter, probably the salts of lime and magnesia, does not exceed two and eight-tenths grains in the gallon ; a quantity, he observes, so small, that a considerable quantity of the water would be necessary to determine the proportions. About two grains of vegetable matter were also suspended in the water, in consequence of the rapid current in which it was taken up, and which would of course subside in the receiving reservoir." The Report next proceeds to speak of the Bronx, and of the capabilities of, and ob- jections to, that source of supply. The lower line taking the water from the Bronx near the mouth of the stream, so as to leave Underhill's Mill and the valuable cotton factory at Tuckahoe, untouched, would reach the bank of the Harlem river at 50 feet above tide. But it being- required to deliver the water in the receiving reservoir at 123 feet above tide, reliance must be had on the power of the Harlem to raise it 73 feet. Upon calculating this power, however, it was found incapable of raising more than 5,000,000 gallons daily, and as this would leave a deficit, even for present purposes when the work should be finished, of two or three millions of gallons a day, it was thought unnecessary to pursue the examination of that route. Another line commencing at Popham's Calico Factory, was carefully surveyed. By rebuilding and raising the dam, a head of 142 feet above tide would be obtained, and no serious obstacles occur in the route before intersecting those laid out for the Croton. But upon guaging the streams of supply, it was at once perceived that no reliance could be placed upon a sufficient quantity from them. " On the 15th of August," says Maj. Douglas, " I guaged the outlet of the Rye ponds, and found it discharging 950,400 gallons per day. On the 20th, and again on the 5th September, it was discharging very nearly the same quantity ; but' between the last two dates, a period of 15 days, it had fallen, having been drawn down by the proprietor two and six tenths inches. This draught, calculated upon the surface of the pond, — 205 acres, gives a daily CROTON AQ.UEDUCT. decrease of 957,500 gallons in the volume of the pond ; showing that, during the time ob- served, the supplies of the pond, from whatever quarter they come, were in quantity about 7,000 gallons per day less than the evaporation. By damming the valley, about three-fourths of a mile below the small pond, so as to back up the water to three feet above the ordinary level of the upper pond, a reservoir of 360 acres will be formed ; and by deepening the outlet of the upper pond, so as to command a draught of five feet in all, we shall obtain a volume of 705,672,000 gallons, or