Please excuse this inroad upon your time, and give to the subject only such attentions as you think its intrinsic importance demands.

Yours, most faithfully,

JOHN A. ANDREW.

[Indorsement.]

GOVERNOR: I have the honor to acknowledge the receipt of your communication of the 27th instant, and have reason to believe that this project has already received great attention.

[G. V. FOX,

Assistant Secretary of the Navy.]

Memorandum for Mr. Fox.*

JANUARY 28, 1862.

Fort Jackson is a bastioned pentagon, with fronts of about 110 yards. It is built of brick and is in good condition. Its scarp walls are 22 fleet high, measured from the offset of the foundation, which is pretty nearly the bottom of the wet ditch. The work is surrounded by a wet ditch, which at the lowest water of the ditches (the ditch water fluctuates abut 16 inches, standing 1 foot higher than low water of river and about 32 inches lower than high water of river, which rises and falls here 5 feet) is 6 feet deep in the middle and about 5 feet at foot of scarp wall. (There is no counterscarp wall, the wet ditch being reverted with timber just up the edge of the water, from where the earth slopes less than 45 deg.) Thus the top of the scarp is 16 feet above surface of water in ditch at low water, and 14 feet 8 inches at high (ditch) water. The ditches are flanked by a 24-pounder howitzer in casemate in each of the ten flanks.

Owing to the fact that the parapets are not carried around the flanks and faces of the bastions (for fear they would not sustain the weight) there is not much room for musketry fire on the flanks. A half dozen riflemen might be stationed behind the top of the scarp, probably, of each flank.

The faces of the bastions may be lined with infantry, as the bastions are followed out, leaving the top of the scarp to serve as parapet. The backs of the caseman arches interfere very much with this arrangement along the flanks.

The two curtains bearing on the river are casemated for eight guns each. As the traverse of a casemate gun is but 60 deg., it follows there is a sector of 12 deg. in front of the central water bastion which is not touched by casemate fire.

The parapets of the two water fronts are arranged to receive twenty-two channel-bearing guns. The parapets of the other fronts receive sixteen more barbette guns, a portion of which bear indirectly upon the channel.

The three land fonts of the work are covered by a glacis-coupe with a covert way, having places of arms in front of the curtains. The two terminating branches of this covert way look upon the channel, and are arranged for wight or nine guns in each.

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* Referred to in Barnard's letter, Series I, Vol. VI, p. 684, but not found in time for publication therewith.

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