I again intrude upon you the subject of the duplicate under cover, which presents a spectacle of human depravity, to excite our sorrow, indignation and abhorrence.

Many circumstances have intervened since my last, confirmatory of the information previously received, and demonstrative of a deep, dark and wicked conspiracy. My doubts have ceased, and it is my opinion, that nought but an immediate peace in Europe can prevent an explosion which may desolate these settlements, inflict a deep wound on our republican policies, involve us in a foreign conflict, and shake the Government to its very foundation.

I received from a correct source the information under cover, at Natchitoches on the 6th instant, and make no question of the facts, though I trust the report of the agent alluded to was a mere “ruse de guerre” to popularize and gain auxiliaries to the real design, “to seize on New Orleans, revolutionize the territory, and carry an expedition against Mexico by Vera Cruz.” This is indeed a deep, dark and wide spread conspiracy, embracing the young and the old, the democrat and the federalist, the native and the foreigner, the patriot of ’76 and the exotic of yesterday, the opulent and the needy, the ins and the outs; and I fear it will receive strong support in N. Orleans, from a quarter little suspected, from whence I have been recently addressed by a Gallo-American, formerly distinguished at Olmutz in a better cause. By masking my purposes and flattering his hopes, I expect to discover the extent and leading characters of the combination in that city; and, till this is effected, I shall carry an equivocal exterior to every person who may see me, excepting my confidential officers.

My letter to the secretary of war will expose to you my military movements and intentions, which may, I hope, meet your approbation; and I intreat that you may be pleased to order him to honor the drafts which may be made on him, for materials and other disbursements essential to the fortifying the city of New Orleans, to enable me to defend it, to repulse the assailants, and command the pass of the river.

You will perceive on inquiry that my means are greatly deficient, but may rest satisfied that nothing shall be omitted which can be accomplished by indefatigable industry, incessant vigilance and hardy courage; and I gasconade not when I tell you, that in such a cause, I shall glory to give my life to the service of my country; for I verily believe such an event to be probable; because should seven thousand men descend from the Ohio, and this is the calculation, they will bring with them the sympathies and good wishes of that country, and none but friends can be afterwards prevailed on to follow them: with my handful of veterans, however gallant, it is improbable I shall be able to withstand such a disparity of numbers; and it would seem we must be sacrificed unless you should be able to succour me seasonably by sea, with two thousand men and a naval armament, to command the mouth of the Mississippi.

To give effect to my military arrangements, it is absolutely indispensible, N. Orleans and its environs should be placed under martial law; for without this, the disaffected can neither be apprehended nor banished; private property can neither be appropriated nor occupied for public purposes; the indiscriminate intercourse between town and country cannot be restrained, and my every disposition will of course be hourly and daily exposed to my adversaries. To effect this necessary measure, I must look up to your influence and authority. To insure the triumph of government over its enemies, I am obliged to resort to political finesse and military stratagem. I must hold out false colors, conceal my designs, and cheat my adversaries into a state of security, that when I do strike, it may be with more force and effect; and therefore my own bosom, were it possible, should be the sole repository of my determination. But independent of considerations of policy, my personal safety will require the most profound reserve, to the last moment of indecision; for were my intentions exposed, there are more than three desperate enthusiasts in N. Orleans, who would seek my life, and although I may be able to smile at danger in open conflict, I will confess I dread the stroke of the assassin, because it cannot confer an honorable death.

Having put the front of the troops in motion for New Orleans under Major Porter, and made arrangements for the rest to follow under colonel Cushing, I left Natchitoches on the 7th instant, and arrived here the 11th to pick up what intelligence I could of the doings above; to sound the public mind; to require a body of militia from the governor, and above all, to find some intelligent confidential agent, who would convey this despatch to you with certain oral communications, which I dare not letter, because nothing less than an overt act will, in my Judgment, warrant the official commitment of names, and none such has as yet been committed, within my knowledge.

Mr. Briggs, with whose good sense and integrity I have been long acquainted, is the only person to whom I could venture to confide the important commission; and he, at my pressing instance, under the assurance I have ventured to make him of your approbation, has agreed to absent himself from his office, under some feigned pretext, and to hand this to you; and to guard against the loss of life or limb, and the casualties of disease, I have associated an attendant with him, who will proceed with my paquet in case any accident should happen to Mr. Briggs.