Beauregard relieved of command.—A letter sent to President Buchanan by Beauregard’s brother-in-law, Senator Slidell, to whom he owed his appointment.

Washington, January 27,1861.

MY Dear Sir,—I have seen in the Star, and heard from other parties, that Major Beauregard, who had been ordered to West Point as Superintendent of the Military Academy, and had entered on the discharge of his duties there, had been relieved from his command. May I take the liberty of asking you if this has been done with your approbation?

Very respectfully yours,

John Slidell.

The President replies on January 29th.