points early in August. The others were taken up as speedily as the clearing of the woods and the means at our disposal would admit, and the gaps in the line afterwards partially filler up by constructions of Fort Gaines, Forts de Russy, Slemmer, and Thayer. The works mentioned are at this date essentially completed and armed, though there is still considerable to do in auxiliary arrangements. Our first ideas as to defensive works beyond the Anacostia contemplated only the fortification of the debouches from the bridges (Navy-Yard Bridge and Benning's Bridge), and the occupation of the heights overlooking the Navy-Yard Bridge. With that object Fort Stanton was commenced early in September. A further examination of the remarkable ridge between the Anocostia and Oxen Run showed clearly that, to protect the navy-yard and arsenal from bombardment, it was necessary to occupy an extent of 6 miles from Berry's place (Fort Greble) to the intersection of the road from Benning's Bridge (Fort Meigs)..

Forts Greble and Carroll were commenced in the latter part of September, and Fort Mahan, near Benning's Bridge, about the same time. Forts Greble and Stanton are completed and armed; Forts Mahan and Carroll very nearly so. To fill up intervals or to sweep ravines not seen by the principal works, Forts Meigs, Dupont, Davis, Baker, Good Hope, Battery Ricketts, and Fort Snyder have been commenced, and it is hived may be so far advance before the winter sets in as to get them into a defensible condition. The occupation of the Virginia shore at the Chain Bridge was essential to the operations of our army in Virginia. It was only delayed until our force was sufficient to authorize it. General Smith's division crossed the bridge September -, and Forts Ethan Allen and Marcy were immediately commenced and speedily finished..

A few weeks later (September 28) the positions of Upton's and Munson's Hills and Taylor's Tavern were occupied and Fort Ramsay commenced on Upton's Hill. The enemy's works on Munson's and the adjacent hill were strengthened and a lunettes built near Taylor's Tavern..

Comprised in the foregoing categories there are twenty-three field forts south of the Potomac, fourteen field forts and three batteries between the Potomac and Anacostia, and eleven field forts beyond the Anacostia, making forty-eight field forts in all. These vary in size from Forts Runyon, Lyon, and Marcy, of which the perimeters are 1,500, 937, and 736 yards, down to Forts Bennett, Haggerty, and Saratoga, &c., with perimeters of 146, 128, and 154 yards. The greater portion of them are inclosed works of earth, though many-as Forts Craig, Tillinghast, Scott, &c., south of the Potomac, and Forts Saratoga, Gaines, &c., on the north-are lunettes with stockaded gorges. The armament is mainly made up to 24 and 32 pounders on sea-coast carriages, with a limited proportion of 24-pounders siege guns, rifled Parrott guns, and guns on field carriages of lighter caliber. The larger of the works are flanked, but the greater number are not, the sites and dimensions not permitting. Magazines are provided for one hundred rounds of ammunition, and may of the works have a considerable extent of bomb-proof shelter, as Forts Lyon, Worth, and Ward, in the bomb-proofs of which probably one-third of the garrison might comfortably sleep and nearly all take temporary shelter. In nearly all the works there are either bomb-proofs like the above, or log barracks, or block-houses of some kind..

It would be impossible to go into any details about these constructions. I am in hopes ultimately to be able to deposit in the Engineer Office drawings of each work with sufficient detail for most purposes..