An abundance of water delivered by gravity under high pressure is usually regarded as one of the essential factors in hydraulic-fill dam building, but it is not essential that there be a large continuous flow. The Lake Frances Dam, recently constructed for the Bay Counties Co., of California, by J. D. Schuyler, is 75 ft. high, 1,340 ft. long on top, and contains 280,000 cu. yds. The dam was built up by materials sluiced by water that was forced by a centrifugal pump through a 12-in. pipe and 3-in. nozzle, against a high bank, whence the materials were torn and conveyed by the water through flumes and pipes to the dam. About 6 cu. ft. per sec. of water was thus used, and at one stage of the work the supply stream was reduced to less than 0.1 ft. per sec., the water being gathered in a pond and pumped over and over again. The chapter on hydraulic-fill dams in Mr. Schuyler’s book on “Reservoirs for Irrigation” will be found to contain matter on the subject interesting to those who desire to pursue it further, and the reader is again referred to that work. An Impervious Diaphragm in Earth Dams. As a result of the recent extended discussion concerning the design of the New Croton Dam and the Jerome Park Reservoir embankments, the Engineering News of Feb. 20, 1902, contained a very suggestive editorial entitled, “Concerning the Design of Earth Dams and Reservoir Embankments.” The opinion is given that no type of structure that man builds to confine water can compare in permanence with earth dams, after which the following pertinent questions are asked: 1. How shall an earth dam be made water-tight? 2. What is the office and purpose of the masonry core wall? 3. Would not a water-proof diaphragm of some kind be better than a core wall of either masonry or puddle? The article then suggests a number of designs of diaphragm construction, with a special view of obtaining absolute water-tightness, by use of asphaltum, cement mortar, steel plates, etc. Special emphasis was put upon the _principle_ of constructing a water-proof diaphragm. The matter of relative cost is advanced as an argument in favor of the diaphragm principle as against the usual orthodox method. The saving in cost is to be accomplished by the use of inferior materials and less care in the handling of them, or by both. It is suggested that almost any kind of material available, rock, sand or gravel, will answer every purpose where good earth is not to be found. Further, that this material may be dumped from the carts, cars or cableways, or be placed by the hydraulic-fill method. The writer believes the diaphragm method of construction may have some merits, but that it is attended by the very great risk of neglecting principles most vitally important to the successful construction of high earth dams, which will now be formulated and advanced, as follows: CHAPTER VI. _Conclusions._