WASHINGTON, D. C., September 23, 1861.

Honorable WILLIAM H. SEWARD,

Secretary of State, Washington, D. C.

SIR: On the 11th instant in pursuance of the orders of the Honorable Simon Cameron, Secretary of War, and Major-General McClellan I went to Baltimore, accompanied by a sufficient number of my detective force and Lieutenant W. M. Wilson, of the Fourth U. S. Cavalry. On Major-General Dix and order from the War Department for the arrest of T. Parkin Scott, S. Teackle Wallis, Frank Key Howard, T. W. Hall, Henry May and H. M. Warfield. The said order mentioned to General Dix that I was directed to conduct the arrests, also to search for and seize the correspondence of the above-named parties.

On consultation with General Dix it was deemed advisable as it was now about midnight to postpone the attempt to arrest until the following night as it was impossible to tell if the parties to be arrested were in town or at their respective houses. General Dix directed me to call on Provost-Marshal Dodge and Assistant Provost-Marshal McPhail, of Baltimore, who would furnish me all the police force necessary to make the arrests. On the morning of the 12th instant I called on Messrs. Dodge and McPhail. I found them to be highly intelligent and able men for their respective positions, and arrangements were at once entered into between us for procuring the necessary information in relation to the probable whereabouts of the parties named to be arrested and the hour of midnight was fixed upon as the time to make the descent, Mr. McPhail detailing a sufficient police force to accompany my own force to each house.

At about 9. 30 p. m. while at the provost-marshal's office an order was received from Major-General Dix addressed to Provost-Marshal Dodge directing the arrest of George W. Brown, W. G. Harrison, Lawrence Sangston, Ross Winans, J. Hanson Thomas, Andrew A. Lynch, C. H. Pitts, L. G. Quinlan and Robert M. Denison. Arrangements were at once made for the arrest of the above-named parties which was accomplished during the night and early on the following day (13th) they were all committed to Fort McHenry.

At about midnight the several divisions moved simultaneously upon the places where we had discovered Scott, Wallis, F. Key Howard, Hall, May and Warfield, and at that time all the above-named were arrested within fifteen minutes, their clothing thoroughly searched and immediately thereafter they were forwarded to Fort McHenry in separate carriages. My force made dilligent search for all correspondence on the premises of each of the parties all of which was seized.

Frank Key Howard being one of the editors of the Baltimore Exchange newspaper and T. W. Hall editor of the South, I construed the order to search for and seize correspondence of a treasonable nature in the possession of the parties arrested a sufficient warrant for me to enter and search the editorial and press rooms of the Exchange and South which I did, seizing the correspondence found therein.

All the correspondence found I brought with me to Washington and now beg leave respectfully to submit to you briefs of the same which I have had carefully prepared, retaining originals in my possession subject to your order.

Very respectfully, your obedient servant,

ALLAN PINKERTON.