only with the suspension of labor on the canal, January 1, 1865. There were thrown in the vicinity of the working parties over 20,000 shells during the whole period of the work. The canal was excavated mainly by soldiers and partly by dredges. The latter were old and almost worn out, and were worked by civilians, who did not come up to their promises, being driven off and frightened by the enemy's shells. Not more than 6,000 to 7,000 cubic yards were removed by the dredges, which were promised to remove 400 cubic yards every ten hours. They worked from the south mouth 200 feet up into the canal, where an embankment separated the part on which the soldiers were working from the lower half.
The whole canal, except an embankment at the north mouth to protect against direct firing, was excavated to the required dimensions. The soil was very favorable below high-water mark. It was the "hardpan" of miners-a hard, stiff, blue clay, perfectly impervious to and insoluble in water. Whatever leakage took place through the strata of sand and gravel was removed by a steam pump.
About the middle of December the mines which had been made in the embankment were nearly completed. This embankment was much larger than was intended to be blown out with powder, for it had been General Michie's endeavor to reduce it far below what would have been almost certain to be removed, but during his absence the water had been let into the excavated part and up to the embankment without orders. It would have required a greater amount of labor and length of time to remove it than we were warranted to use at this period.
It remained then only to do the best to blow out the mass between the water in the river and that in the canal; and the problem became to use an amount of powder large enough to remove the embankment and disturb its foundation so that it would be easy to remove afterward and, at the same time, not so much as to disturb and cave down the walls of the canal in the vicinity. Twelve thousand pounds of powder were divided among five mines-one of 4,000 and four of 2,000 each-distributed as follows: Three mines were placed at a depth of fifteen feet below high water, one of 4,000 being on the center line of the canal and thirty-five feet from the face of the embankment, and two of 2,000 each were placed on the same level ten feet on each side of the center line and twenty-five feet from the face. Two remaining were at a depot of twenty-five feet below high-water mark, or ten feet lower than the three first, and twenty feet farther out than the central mine toward the channel on the north side.
Toward the time of charging and tamping the mines the water leaked in very rapidly and the pumps were kept going night and day. The powder in the four smaller mines was in tin cans holding 125 pounds each. In the larger mine the powder was in four large rubber bags holding 800 pounds, and in the center of which was the point of fusion of this mine.
The method of exploding the mines was by means of the Gomez fuse, a quick-burning composition said to be instantaneous for distances under 100 feet. This method proved defective, and the results showed conclusively that all of the powder did not burn, and will not when ignited in the center of large mines. The effect would, in General Michie's opinion, have been several times greater if centers of fusion could have been made for every hundred pounds of powder, which can be done now with an electric apparatus.