Fourth. The salient, formed by the redoubt at the angle of the enemy's line, flanks part of the line in front of the Ninth Corps. Its distance from the line of the Fifth Corps varies from 400 to 800 yards. From the salient to the redoubt south of it, some 500 yards, the works face a space of apparently smooth open plain. Between the Fifth Corps and the salient a ravine commences, rapidly deepening becomes quite deep in front of the Ninth Corps, which has passed it at one point and effected a lodgment within about 150 yards of the enemy's line and immediately in front of one of his batteries. Toward this General Burnside is running a mine, with the intention of destroying the battery and immediately assaulting the works, and if possible gaining the crest overlooking Petersburg.

Fifth. To render an assault successful, it is necessary to destroy the obstructions, abatis, palisades, &c., in front of this line, to silence, if practicable, the guns, and especially to capture or effectually silence the redoubt at the salient of the enemy's line, which not only flanks that line, but sweeps the ground on which the supports to the assaulting column must pass.

Sixth. To destroy or to occupy the salient regular approaches are the proper means. The ground in front is favorable as a whole, and in the reports of the chief of artillery and myself of the 6th instant this plank was proposed. The recent reduction of force of the army will not, it is understood, permit the occupation of any ground in front of the south line of the enemy's defenses, and we are therefore limited to such operations as we can effect on a line parallel to that of the enemy facing east.

Seventh. To effect this the lines now occupied by the Fifth Corps should be advanced as far as practicable, if possible to the edge of the ravine before mentioned, and as much artillery as can be safely and advantageously used place in battery. Artillery should also be placed in position in Burnside's front, not only for his direct fire, but to bear upon the salient and batteries in front of the Fifth and Eighteenth Corps.

Eighth. The enemy's fire being silenced approaches should be made if practicable across the ravine, and possession so gained of the angle, and the way cleared at the same time for the assault by the Ninth Corps. The mine should not be sprung until all the preparations for an assault are made.

Ninth. The crest above the enemy's present line may be crowned with batteries by him. Its possession gives the defense great advantage over the attack. If the assault is successful an immediate and vigorous attempt should be made to get possession of the crest. Should it fail the assaulting troops should make good a lodgment as far in advance as practicable, and operations be continued from the salient to get possession of the crest behind it. To do this it will probably be necessary to occupy more ground to our left.

Tenth. Should these operations offer to the enemy in front of the Eighteenth Corps means of annoyance, which are not at present very apparent, the necessary measures must be taken to overcome them as they develop themselves.

Eleventh. The advantages of position on the part of the enemy, with the restricted numbers which will prevent our making use of the ground which would envelop him, will make the success of our operations difficult, and probably costly, both in line and men.

J. C. DUANE,

Major of Engineers.

HENRY J. HUNT,

Brigadier-General and Chief of Artillery.