[Inclosure.]

Extract from letter of Bvt. Major General M. C. Meigs, dated Washington, D. C., July 16, 1864.

Twice while McClellan was on his way to the James, or there, they did by the Shenandoah put Washington in danger; but there were troops here then to defend it; now with an enterprising and uniformly successful commander, a larger army, trained to confidence and success through three years of doubtful conflicts and two months of most bloody, desperate, and successful fighting, the crippled army of Lee, relying upon the intrenchments of Richmond and the weakness of the Washington garrisons, sends again by the familiar road a column of 25,000 or 30,000 men, breaks communications north and east of Baltimore, defeats a veteran division of the Army of the Potomac (Ricketts') hastily thrown across the line of march, drives Wallace and Ricketts back upon Baltimore, and sending small parties to alarm and raise the neighborhood, to burn the house of the Governor, and prevent the troops of the north passing beyond, alarmed Baltimore; this column concentrates suddenly upon the north front of Washington. The invalids, now called Veteran Reserves, of the police garrison of Washington, are relieved from guards duty by the clerks of the Quartermaster-General's Office. The old soldiers in hospital and in convalescent and distribution camps are hastily organized into provisional regiments, dismounted cavalry-men, for whom horses are not here, are sent into the trenches to act as infantry, and the mechanics, agents, clerks and overseers, and laborers of the depot quartermaster, who can for a day or two in emergency be detached from their ordinary duties, are organized and armed, and marched to the trenches. The head of the column of the Sixth Corps of veterans from the Army of the Potomac arrives from Petersburg on the day that the head of the Nineteenth Corps reaches Washington from New Orleans, and on the very day that the rebels send their skirmishers within forty rods of the salient of Fort Stevens, and within sight of Fort ReNumbers The former on the Seventy-street road, and the latter on the Rockville or Tennally-town road.

On Monday morning at daylight our cavalry was sent out the Tennally-town road to force the enemy to develop himself in line of battle. A handsome skirmish showed at this point in front of Reno about 1,200 cavalry and a horse battery. Later in the day General McCook reported the rebels were advancing in force. I had offered the services of the quartermaster's men, of whom we had about 3,000 armed, who were disposable for this purpose, to General Halleck. He thought that it would be enough for them to guard the stores in the city against riot or incendiary attempts. I then offered them to General Augur, commanding the forces, and he gladly accepted them and requested that they be sent to Major-General McCook at Fort Stevens, on the Seventh-street road. I called the men out; 400, who were under General Augur's quartermaster, had been sent out in the morning, 700 more had gone to the lines in front of Alexandria, and I marched about 5 p. m. with 1,500 or 2,000 toward Fort Stevens. Reported to McCook just as it grew dark, and he sent an officer from Fort Slocum to point out the position he wanted us to occupy. We found it as well as we could in the darkness. The new moon gave a little light and our forces, which the next morning numbered 1,500,