63. On the mud there is a growth of very coarse grass, Spartina glabra and Uniola spicata, which is 4 or 5 feet high. It does not, however, form a sod, and the roots are not deep, but fine; they afford but little resistance to anything sinking through them. Extreme high water covers the surface of the mud.
64. Geologically the marsh is held to be sedimentary deposits of the very finest particles, brought down by the fresh-water streams, and are mostly vegetable. The blowing sands from the outer beaches, which are less recent in their formation, are sometimes mixed with the mud.
65. The resistance is increased by quantities of small shells, Auricula bidentata and Littorina irroratus, and occasionally muscles.
66. Some idea of the extreme softness of the marsh can be formed by the extent that a couple of men on a plank resting on the surface can shake it, by surging themselves abut.
67. The vibrations extend over many hundreds of square yards, as if they were on jelly.
68. A general idea of the kind of structure to be built having been formed, preparations were made to obtain the necessary material, and provide the means of getting it on to the ground.
69. The commanding general having ordered that the work should be made suitable for one 200-pounder Parrott rifled gun, and that it should be placed as near to the city of Charleston as practicable, on our side, however, of the stream next southeasterly from Light-House Creek, it became evident that whatever details of plan might be adopted, the general features of the localities being similar, the primary arrangement would remain constant, wherever the position might be finally determined upon.
70. During the time that preceded the approval of the plan and the commencement of the work on the ground, but after it had been determined to make a battery on the marsh, at some advanced point, the causeway before described leading from the left center batteries to Black Island was in progress of construction.
71. Finding it practicable to build this road under the enemy's fire, which was sometimes quite heavy, it became apparent that it might be made use of, in part, at least, to facilitate the erection of the other work, and it thence forward entered into the plan of operations.
72. As it seemed settled that whatever arrangement might finally be approved would involve the use of large timber in great quantities, working parties were sent to Folly Island, at the nearest point where suitable trees could be found, to cut and prepare them and bring them forward ready for use; and as it was determined that the whole parapet must be made of bags filled with sand, a point was selected near the old camp of the engineer troops, and working parties, superintended by the volunteer engineers, were employed day and night filling bags and hiding them from the enemy's view, under cover of the bushes and ridges.
73. The old engineer camp was selected for this purpose, because it was one of the two points farthest advanced into the marsh, in the right direction, and afforded plenty of good material and water communication to the battery to be constructed, wherever it might be, between it and Charleston Harbor, on any part of the marsh, if upon the edge of any of the streams.
74. In order to determine the sustaining qualities of the marsh, and to ascertain what uniformly distributed weight might safely be