FORT LAFAYETTE, November 29, 1861.

Honorable WILLLIAM H. SEWARD, Secretary of State.

SIR: On the 20th instant in the city of Detroit, Mich., I was suddenly arrested without being informed of the charge against me further than the general one of disloyalty. Knowing that I had laid myself liable to suspicion by an act of inconsiderate folly I was most anxious for an immediate examination. This favor was refused me and I was immediately sent to this post. I am anxious to make a full and explicit report of what I know, not I beg you to believe to screen myself but to prevent if possible suspicion falling upon loyal and innocent men. If I were alone interested I believe rather than confess my knowledge of the cause of my arrest and the trouble I have unwittingly occasioned I would prefer running my chance under an unsupported charge of disloyalty, but the interest of others demands that I should admit not my guilt but my folly.

My only guilt, sir, lies in attempting to play off a practical joke upon the Detroit press. It is impossible that in the short space of a few months all old party animosities and prejudices should be forgotten. Although the Democratic press and people acquiesce with mroe or less cordiality in the policy of the Administration still beneath it all there is an undercurrent on minor subjects of political rancor which still maintains old party lines. Actuated by such feelings the Democrants charge the Republicants with abolition, while the Abolitionists without any show of reason charge all Democrats with either disaffection to the Government or outright treason. In Lapeer County, Mich., in particular, remote from the wild whirl of political and warlike events, these feelings exist in all their strength - so much so indeed that there is scarcely any communication between members of the two parties.

Some time in September, I think, my enemies having reported me a secessionist, my office was attacked in the night and ransacked and other acts of violence committed, of course by Abolitionists. About the same time I noticed frequent paragraphs in the Detroit papers charging the Democrants with treason, with oft-repeated reference to a secret league favorable to the Confederate States. These events, the accusation of men whom I admired as statesmen and loyal Americans, the disgrace heaped upon me by Canadian abolitionists, who I knew at heart bore little love to my native country, living remote from civilization, and although reading not realizing the fearful change which has taken place in the past six months; the unviersal reign of suspicion, revenge and a desire to sell the Detroit treason-shrieking press - all this and many influences which I will not occupy your time in rehearsing, on reading a very irritating paragraph on Democratic treason, it suddenly entered my mind to sell the Detroit press by writing a letter full of dark innuendoes and hints, but which in reality would mean nothing. The idea was hardly conceived before it was executed.

My only fear in writing it was that it would be immediately seen through, and I caught at every circumstances which would add to its plausibility without for a moment considering that I might be weaving a web not only to catch myself in but one which would be very difficult to unravel. My furthest expecation was that it would be sent to one of the treason-shrieking presses, and when exploded would produce lots of fun. I fancied such a sell would be apt to quiet their howls. My only belief was that it would be either immediately seen through or if the fish took the bait it would be sent to the Tribune, drawing from that admirable journal and yell and intense satisfaction.