Mr. Strange recommends filling the puddle trench with material having three parts soil and two parts sand. After the first layer next to bed rock foundation, which he kneads and compacts, he would put the layers in dry, then water and work it by treading, finally covering to avoid its drying out and cracking. Prof. Philipp Forchheimer, of Gratz, Austria, one of the highest authorities and experimentalists, affirms that if a sandy soil contains clay to such an extent that the clay fills up the interstices between the grains of sand entirely the compound is practically impervious. Mr. Herbert M. Wilson, C. E., in his “Manual of Irrigation Engineering,” recommends the following as an ideal mixture of materials: Cu. yds. Coarse gravel 1.00 Fine gravel 0.35 Sand 0.15 Clay 0.20 –– Total 1.70 This mixture, when rolled and compacted, should give 1.25 cu. yds. in bulk, thus resulting in 26½% compression. Mr. Clemens Herschel suggests the following test of “good binding gravel:” “Mix with water in a pail to the consistency of moist earth; if on turning the pail upside down the gravel remains in the pail it is fit for use, otherwise it is to be rejected.” For _puddling material_ he would use such a proportion as will render the water invisible. CHAPTER IV. _The Tabeaud Dam, California._ The Tabeaud Dam, in Amador County, Cal., built under the supervision of the author for the Standard Electric Co., is an example of the homogeneous earth dam. A somewhat fuller description and discussion will be given of this dam than of any other, not on account of its greater importance or interest, but because it exemplifies certain principles of construction upon which it is desired to put special emphasis. This dam was described in Engineering News of July 10, 1902, to which the reader is referred for more complete information than is given here. [Illustration: FIG. 3.–PLAN OF TABEAUD RESERVOIR, WITH CONTOURS.] [Illustration: FIG. 4.–PLAN OF TABEAUD DAM, SHOWING BED ROCK DRAINAGE SYSTEM.] [Illustration: FIG. 5.–DETAILS OF BED ROCK DRAINS AT THE TABEAUD DAM.]