HEADQUARTERS DEPARTMENT OF THE PENINSULA,
Yorktown, Va., March 6, 1862.

General S. COOPER,

Adjutant and Inspector General C. S. Army:

SIR: The telegram, informing me that the Baltic, with three regiments on board, had left Newport News, has just been received.

Mr. William Norris, my signal officer at Sewell's, had reported the arrival at Newport News of troops within the last week in large numbers, estimated by me at six regiments, in addition to six companies of light artillery, with their horses.

In pursuance of the orders of the Secretary of War, to so dispose my forces as to throw re-enforcements across to Suffolk, I withdrew the troops from Harrod's and Young's Mills, except the cavalry and one regiment of infantry at each place. it was almost impossible to withdraw the artillery on account of the state of the roads. I have arranged the remaining troops not in garrisons, about 4,000 men, on the second line, and informed Captain Buchanan that for the above reasons I would not be able to have my troops down in the neighborhood of Fort Monroe and Newport News should he attack the two frigates at the latter place. It of course could not have been supposed that I could do so, when the department ordered away from me more than one-half of my force disposable for the field, even if the state of the roads permitted it. The shorter line, which I now occupy, will be defended with a force totally inadequate for that purpose.

The Merrimac will make no impression on Newport News, in my opinion, and if she succeeds in sinking the ships lying there it would do us little or no good, but if she had attacked the Baltic and other transports filled with troops in those waters here success would have been certain and of incalculable advantage to us. Please ask the Secretary of War to impress these views on the Navy Department.

To make up the 5,000 men ordered to Suffolk I have been compelled to send the following regiments an corps, which are now marching to King's Mill, to proceed via City Point and Petersburg, viz: Cobb's Legion, Sixteenth Georgia Regiment, Second Louisiana Regiment, Fifteenth North Carolina, and Fifty-third Virginia Regiments. In Cobb's Legion is included one field battery and about 350 cavalry, and I have sent an additional field battery.

You will perceive that nothing can be done by me in the way of an attack after having parted with so large a portion of my army. Indeed, unless some important object could be attained, the policy of merely being present near Fort Monroe and Newport News when the latter is bombarded is exceedingly doubtful, as it would incur a risk of disaster without any corresponding advantage, and especially as the number of troops at both places is increased, notwithstanding the recent departures, while my own is diminished by more than one-half disposable for field service. In any event I could render no assistance to the Merrimac merely by my presence. these are my views, and I think they are those of every officer under my command. I will execute however with alacrity any orders which may be given.

I have the honor to be, sir, very respectfully, your obedient servant,

J. BANKHEAD MAGRUDER,

Major-General, Commanding.

P. S.- The negroes are coming in pretty rapidly.