glance at the map will show it to be almost a continuous forest. It is not deemed necessary to connect the works by a continuous line of parapet, but the intervening woods should be abatises and open ground traversed by a line of artificial abatis, and infantry parapets, half-sunk batteries, &c., placed so as to protect these obstructions and to see all the irregularities of the ground not now seen from the works. Considerable work is also required in the way of roads, the amount of which I cannot state with any precision. Several miles of roads have actually been made. The works themselves would be very much strengthened by caponiers in the ditches, additional internal block-houses, or defensive barracks, &c..

The aggregate perimeter of all the works is about 15,500 yards, or nearly 9 miles, including the stockaded gorges, which, however, form a small proportion of the whole, requiring, computed according men to the rule adopted for the lines of Torres Vedras, 22,674 men (about for garrisons..

The number of guns, most of which are actually mounted, is about four hundred and eighty, requiring about 7,200 men to furnish three reliefs of gunners. The permanent garrisons need consist to only these gunners, and even in case of attack it will seldom be necessary to keep full garrisons in all the works..

The total garrisons for all the works (one hundred and fifty-two in number) of the lines of Torres Vedras amounted to 34,125 men; and as the total perimeters are nearly proportional to the total garrisons, it appears that the lines about Washington involve a magnitude of work of about two-thirds of that in the three lines of Torres Vedras..

The works themselves, fewer in number, are generally much larger than those of Torres Vedras, and involve, I believe, when the amount of bomb-proof shelter in ours is considered, more labor per yard of perimeter; but the latter lines involved a greater amount of auxiliary work, such as the scraping of mountain slopes, palisading, abatis, roads, &c., than we have had occasion to make..

The lines of Torres Vedras were armed with five hundred and thirty-four pieces of ordnance (12,9, or 6 pounders, with a few field howitzers); ours with four hundred and eighty pieces, of which the greater number are 32-pounders on barbette carriages, the rest being 24-pounders on the same carriages, 24-pounder siege guns, 10, 20, and 30 pounder rifled guns (Parrott), with a few field pieces and howitzers. As to number of guns, therefore, our armament approaches to equality with that of the famous lines mentioned; in weight of metal more than doubles it..

The above applies to our works as now nearly completed, and has no reference to the additional works I have elsewhere mentioned as hereafter necessary. It is impossible to give any other statement of actual cost of the works than the total amount expended thus far. The work has been done partly by troops and partly be hired laborers, the works north of the Potomac being mostly done by the latter. The large amount of carpentry in magazine frames and doors and blindages, barrier gates, stockades, block-houses, defensive barracks, &c., has kept a large gang of carpenters all the time at work, and caused a large expenditure for lumber. The entire amount made available by the Department for these works has been $344,053.46, and this will all have been expended (or more) by the end of the present month. This would give an average of a little over $7,000 for each of the forty-eight works; but of course the real cost of them has been very unequal..

The importance of perfect security to the capital of the United States in the present state of affairs can scarcely be overestimated, and these.