(1) Insuring a more thorough wetting of the central portion of the dam; any excess of water in this part would be readily taken care of by the central cross drains. (2) In wetting the finished surface prior to depositing a new layer of material, water from the sprinkling wagons would naturally drain towards the center and insure keeping the surface wet; the layers being carried, as a rule, progressively outward from the center. (3) It centralized the maximum earth pressure and enabled the depositing of material in layers perpendicular to the slopes. (4) It facilitated rolling and hauling on lines parallel to the axis of the dam, and discouraged transverse and miscellaneous operations. (5) It finally insured better compacting by the tramping of teams in their exertions to overcome the grade. [Illustration] [Illustration: FIG. 12.–CROSS AND LONGITUDINAL SECTIONS OF TABEAUD DAM.] The specifications stipulated that the body of the dam should be built up in layers not exceeding 6 ins. in thickness for the first 60 ft., and not exceeding 8 ins. above that elevation. The finished layers after rolling varied slightly in thickness, the daily average per month being as follows: April 4 ins. May 3½ “ June 4 “ July 4½ “ August 5 “ September 6 “ October 7 “ November and December 8 “ During the last few months more than one whole layer constituted the day’s work, so that a single layer was seldom as thick as the daily average indicates. It was stipulated in the specifications that the up-stream half of the dam was to be made of “selected material” and the lower half of less choice material, not designated “waste.” “Waste material” was described as meaning all vegetable humus, light soil, roots, and rock exceeding 5 lbs. in weight, too large to pass through a 4-in. ring. It may be well to define the expression “selected material,” so commonly used in specifications for earth dams. In England, for instance, it is said to refer to materials which insure _water-tightness_, while in India it refers to those employed to obtain _stability_. It ought to mean the best material available, selected by the engineer to suit the requirements of the situation. The method employed in building the body of the embankment may be described as follows: (1) The top surface of every finished layer of material was sprinkled and harrowed prior to putting on a new layer. The sprinkling wagons passed over the older finished surface immediately before each wagon-row was begun. This insured a wetted surface and assisted the wheels of the loaded wagons, as well as the harrows, to roughen, the old surface prior to depositing a new layer.