arising from splinters. (In cases there is a heavy artillery fire they may be easily removed.) Second. Their cost is less than one-twentieth that of sand-bags. While sand-bag loop-holes require three and should have five bags, at 50 cents, these cost less than 10 cents per loop-hole. One saw-mill can but boards for 600 or 700 in one day, and the only additional cost is for a few nails.
On the Twenty-fifth Corps front the revetment of the breast-work between Forts Burnham and Brady has been repaired and improved, and the magazine in Fort Burnham lined with boards and covered with an additional depth of earth. As the enemy's artillery in front of this portion of the line consists almost entirely of mortars, some protection other than the ordinary parapet seemed necessary to cover the garrison. During the recent demonstration by the rebel rams the enemy opened twelve or fourteen Coehorn and 8-inch and 10-inch mortars on the fort, and drove the garrison to their bomb-proofs, silencing the artillery. To obviate this difficulty in future, casemates of the plan indicated by the accompanying drawings* have been commenced. One is nearly completed and materials for several others prepared. The damage done to Fort Brady during the recent bombardment has been repaired, and a small sunken battery has been built below the fort on the opposite side of the ravine. The parapet of this work has been made thirty feet thick, in order to withstand the heavy rifle projectiles of the enemy, which have been found to penetrate upwards of Sixteen feet in solid earth. It is proposed to mount a 100-pounder Parrott gun on a Dahlgren carriage, or a 30-pounder on a siege carriage, in this work, so that it may be shifted from one embrasure to another.
On the Bermuda front the following repairs and additions have been made: Battery Pruyn-embrasures repaired, parapet raised one foot, and magazine rivetted and drained; Redoubt Dutton-embrasures repaired, magazine and breast-height revetment rebuilt; Battery Marshall-unimportant repairs; Battery Anderson-new revetment, for embrasures, magazine repaired, and left flank raised, and a new embrasure cut to sweep the ditch of the new line of the left; Battery Drake- repairs to revetment and embrasures; Battery Spofford (water battery)-altered to mount two 100-pounder Parrott guns; both are in position. Battery Sawyer-the magazine and the covered way leading to the battery have been repaired, and the embrasure for the 100-pounder altered to obtain a wider range. A new sunken battery has been constructed about 150 yards to the left of Battery Sawyer, to mount a 100-pounder Parrott gun to command front reach and a portion of the river below. The pile bridge has been completed and the pontoon bridge removed. Drawings+ showing the construction of the bridge and draw are forwarded with this report. This work was superintended in detail by Captain Lyon, Fourth Rhode Island Volunteers, assistant engineer, who deserters great praise for the rapid and workmanlike manner in which it was executed. The bridge is 1,350 feet long, twenty-one feet wide, and about nine feet above low water. The bays are fifteen feet wide, and each supported by three piles. As the water in the channel is about twenty-five feet deep, some of the piles were cut fifty feet long; the greater number being thirty and forty feet long. Owing to the hardness of the river bed it was found impossible to drive piles more than eight or ten feet, and it was also found unnecessary to drive them farther, as they will break off instead of pulling out.
* See Plate LXVIII, Sketch 8 of the Atlas.
+ See Plate LXVIII, Sketch 6 of the Atlas.