narrows so as to expose the slopes in both directions. It commands the three avenues to Washington which unite at Tennallytown. The work, as originally built, was deficient in size; its exposed parapets too thin, and it had not a good view of the approaches from the northward. A battery for eight guns has been constructed on an advanced point of the ridge (say 300 yards northward), with magazine and inclosed gorge. This is connected with the work by a double line of rifle-pits, with a flanking battery, making of the ensemble a very strong position. The armament of the fort has been increased, and its disposition improved; platforms constructed for additional field guns, and a 100-pounder rifled gun mounted to sweep the sector from Fort Marcy to Fort Massachusetts. The Commission recommend an increased thickness for the parapets of exposed fronts, and the construction of a bomb-proof for garrison.

Between Forts Pennsylvania and Kearny is a battery for eight field guns, very substantially constructed, with magazine, but with open gorge. It has good views of the cross valley running from near Fort Pennsylvania to Broad Branch (of Rock Creek),and sees well the ridge of high ground in front of Forts Pennsylvania, Kearny and De Russy. The Commission recommend that its gorge be closed by a stockade, and extend this recommendation to the different batteries of similar construction between Forts Ripley and Massachusetts.

Fort Kearny (recently built), occupying an excellent position, is a necessary connecting link between Forts Pennsylvania and De Russy. It sees well the upper valley of Broad Branch, and crosses its fires with those of Forts Pennsylvania and De Russy and intermediate batteries upon the dangerous heights in front. It has a powerful armament, and is provided with ample magazines and bomb-proofs, and is well adapted to its location. A field battery,just across Broad Branch, has been built to sweep part of the ravine immediately in front of Fort Kearny; otherwise unseen.

Fort De Russy occupies a very commanding point, overlooking the deep valley of Rock Creek, and throwing a cross-fire upon the approaches to Fort Massachusetts, and (together with Fort Kearny) controlling the country roads between the Rockville turnpike and Rock Creek. It is too small, and its fire was inadequate to its position. The site does not admit of an easy extension. This defect is partially remedied by the construction of batteries on either flank,and a few hundred yards to the left, having a better view of the Milk-House Ford road and ravines toward Broad Branch; the other, on the right, sees the slopes toward Rock Creek. The Commission recommend the introduction of a 100-pounder, on center pintle carriage, in place of one of the 32-pounders, to sweep the sector from Fort Pennsylvania to Fort Massachusetts; the fire of which will be particularly important upon the approaches to Fort Massachusetts also; the construction of casemates for reverse fires in the east and west angle of the counterscarp.

Fort Gaines is a work in second line. Should the enemy succeed in forcing the interval between Forts Ripley, and Pennsylvania, he could not establish himself on the secondary ridge, on which Fort Mansfield is situated, under the fire of this work, by the rifled guns of which the magazines of Fort Mansfield may be exploded. The Commission believe nothing further is required at this work.

Batteries Cameroon, Parrott and Kemble.-- The first, of two rifled James 42s, the other two of one 100-pounder each, are designed,, first, to enfilade the front of the Arlington lines from Fort De Kalb to Tillinghast; second, to operate on the heights between Forts De Kalb, and Marcy,