PETERSBURG MINE.
We have been kindly furnished by General Pleasants with the necessary data to present our readers with several interesting illustrations of the celebrated Petersburg Mine, and the triangulation by which the distance and direction were obtained to reach the rebel fort.
It will be noticed by diagrams Nos. 1 and 2 that the fort blown up was concealed behind the front line of rebel rifle-pits or breastworks, and from a front view no evidence of a fort appeared, as the embrasures were concealed. But a distant end-view enabled General Pleasants to locate it, and subsequent demonstration provoked the rebels to unmask.
The sketch of the front or mouth of the mine represents a little hollow below and outside our breastworks, which are represented above covered with sand-bags. Between the mouth of the mine and the breastworks, or rifle-pits, is shown the air-shaft for the ventilation of the mine.
The timbers are represented in the sketch as they were used in the mine,—forming a frame; they were cut, notched, and fitted at a distance, and when taken into the mine were put into their place, and secured by thin wooden wedges, without creating a noise. As at the building of Solomon's temple, "the sound of a hammer was not heard." Four pieces were used,—that is, the cap or "collar," the two "legs," and the "mud sill." These frames were placed about three feet apart, and when the clay or material driven through was soft and yielding, boards or " laggins" were placed behind the timbers. The excavated material—earth, clay, &c.—was taken to the surface in cracker-boxes,
as represented in the sketch.
Figure 164 represents the relative position of the Union and rebel works, the direc tion and form of the mine, and its lateral galleries, in which the powder was laid. The mouth of the mine is represented by 1, the air-shaft by 6, the left chamber, or lateral, by 2, and the right chamber by 3. The rebels sunk a counter-mine at 4; but General Pleasants very ingeniously " surrounded them" by describing nearly a half circle in the right chamber.
This figure also represents the triangulation by which the distance and course were obtained to the rebel fort, as explained below.
Figure 165 represents a section or end-view of the Union and rebel works, and a longitudinal view of the mine. The mouth is in a hollow behind the Union rifle-pits or breastworks G H, under which the mine is driven. It then crosses the intermediate space between the lines, passing the rebel rifle-pits F E, and ending under the fort D C. It is nearly horizontal for over one-third of the distance, but an incline rises near the middle to avoid a tough, hard clay, and runs to a point near the rebel rifle-pits F E, and from thence it was driven level. This elevation brought the interior of the mine only a short distance below the ditch of the fort,—perhaps less than 10 feet.
The air-shaft is represented by 6, and the rebel counter-shaft by 4. Abatis are erected before the Union and rebel works.