placed upon it, a platform of 3-inch plank 4 feet square was made and laid on the natural surface.
75. The platform was then loaded with filled sand-bags, piled with care in regular layers, until a load equal to 400 pounds to the square foot was attained;and although the mud was so soft that the bags could not be carried by the men over it to make the trial, excepting by walking on boards, the column on the platform remained erect, and, after standing twenty-four hours, showed no signs of settlement.
76. The mud was 12 feet deep under the platform where the trial was made.
77. After it had stood for twenty-four hours, additional sand-bags were piled upon the column, and when it reached a height of about 7 feet, corresponding to a pressure of about 650 pounds to the square foot, a tendency to lean on one side was manifested; this, however, was suppossed to be occasioned by the soldiers tramping about near the corner that went down first. The platform seemed to act in the manner of a punch cutting its way into the surface.
78. After about another hour and a half, additional bags were piled upon the column, until a force of about 900 pounds to the square foot on the platform had been obtained, when the whole suddenly upset, throwing the sand-bags over, burying many of the upper tiers, which fell the farthest, out of sight in the mud; the platform, however, sank but about a foot at one corner, and the trial was considered merely as showing that the sustaining strength of the marsh was equivalent to over 600 pounds to the squad foot, where the load is uniformly distributed. The ultimate sustaining strength was not ascertained.
79. This is represented in Plate IV, FIg. 4. The full lines represent the weight equal to 150 pounds, would sink into the mud 18 to 25 inches every step, and, if these were not made with some rapidity, much deeper. Two elements are involved here not in the other case; first, that of the motion of the foot, and, second, the suction of the mud against the leg, one tending to favor the penetration, the other retarding it; neither of these conditions applied where the load was static and rested on the surface.
81. In the case of a man attempting to walk, it wa shown that, under the conditions he presented, something like a force of 500 or 550 pounds to the squad foot could not but sustained by the marsh, but here there was the heavy weight of the body brought on the small point of the toe, or the side of the foot, or upon some other part of the sole of the shoe, in motion. If a battery was to be built, so long as the guns were not fired the forces would essentially be static, and the condition of rest become an important element in the calculation.
82. But guns, to be offensively useful, must be fired, and to fire them while floating, as it were, on the surface of the mud, would produce vibrations. How far these vibrations would affect the stability of any structure so situated was still undetermined.
83. If any machinery like a pile-driver was to be employed to make a foundation, provision must be made to hide it during the day and work it at night, or it would be destroyed by the enemy's fire. So large and unhandy a machine as a common pile-engine could not be used. The time required to set it up and take it down during the