One method adopted in Algeria, which has the advantage of permitting the sediment to be utilized together with the irrigation, this sediment being very fertilizing, is to pump air down through hose extending to the bottom of the reservoir, the pumps being actuated by steam power or turbine, and the sediment thus stirred up and run off with the water through the irrigation pipes.  As an example of one of the early types of masonry dams in France, reference may be made to Fig. 13, on which is shown an elevation and cross section of the Lampy dam, forming a large reservoir for feeding the Languedoc canal.

I will now refer to some of the most notable masonry dams in existence, commencing with France, where perhaps the finest is that known as the Furens, in connection with the St. Etienne Water Works, constructed between the years 1859-66, and designed by the engineers Graiff and Grandchamps.  It is curved in plan, struck with a radius of 828 ft. from a center on the down stream side, and founded upon compact granite, the footings being carried down to a depth of 3 ft. 3 in. below the surface of the rock.  It is of rubble masonry, in hydraulic mortar, carried up in courses of 5 ft. in depth.

The height is 170 ft. on the up stream side and 184 ft. high on the lower side, with a breadth of 9 ft. 8 in. at the crest and 110 ft. at the base, and the cross section is so designed that the pressure is nearly constant in all parts, and nowhere exceeds 93 lb. to the square inch—­13,392 lb. to the square foot.  The contents is equal to 52,000 cubic yards of masonry, and the cost of erection was L36,080.  The capacity of the reservoir is equal to 352,000,000 gallons.

The reservoir discharges into two tunnels (see Fig. 11), driven one above the other through a hill into an adjacent valley.  The lower tunnel contains three cast iron pipes, with a masonry stopping of 36 ft. long.  Two of these pipes are 16 in. diameter, with regulating valves, and discharge into a well, from whence the water can be directed for the town supply or into the river.  The third pipe, of 81/2 in. diameter, is always open, and serves to remove any deposit in the reservoir, and to furnish a constant supply for the use of manufacturers.

The author drew attention to the difference in the section of the Furens dam, Fig. 11, as compared with that of Alicante, and of Puentes, which is similar to the latter.  These two last illustrate the ancient Moorish type, and the former that of the present day.  The Gileppe dam at Verviers, in Belgium, Fig. 14, although quite recently erected, viz., between the years 1869 and 1875, differs very much from the Furens type, in so far as it is of very much larger sectional area in proportion to its height, but this is accounted for by the desire of the engineer, M. Bodson, to overcome the opposition to its construction, and meet the objections and combat the fears of those whose interests—­and those serious ones, no doubt—­would be affected in the event of its rupture, the body of water stored being 2,701,687,000 gallons, or about eight times as much as the capacity of the Furens reservoir.