to the United States, are matters of extensive detail and of abounding evidence. Having appealed to the South for assistance every appearance indicated a rapid accumulation of men and means for seizing Government property and overturning its authority. I accordingly foresaw that under the extraordinary measures of the governor and Legislature of this State aggressions would soon commence against the General Government on the part of these opposers of it, and of all who were in such a state of hostilities, willing to support the State against the Government. Of this there can be no doubt, as also that the issue would be taken by the State as soon as the felt able to sustain it. It was therefore necessary to meet this embaation as early as possible, and accordingly I proceeded yesterday with a large body of troops, supported by artillery, to the camp above referred to, and which is situated in the western part of the city, at what is known as Lindell's Grove, between Olive street and Laclede avenue, and arrived at 3. 15 p. m., and demanded of General Frost, the commander, a surrender of his entire command. Copies of the correspondence are herewith inclosed. *

Of the stores from Baton Rouge Arsenal, as far as understood, there were found three 32-pounder guns, one mortar, three mortar beds, and a large supply of shot and shells in ale barrels. All these artillery pieces were in boxes of heavy plank, and were addressed "Tamoroa, care of Greely & Gale, Saint Louis," "I. C. R. R.," to whom no delivery was made, this being a guise to cover the movement, and Greely & Gale being known as strong Union men saved them from close scrutiny. No doubt many arms, the mortars corresponding to the beds, and other war materials were received, agreeably to numerous reports made, but which can be obtained only by a thorough search over the city. Of the material besides tents, baggage, camp equipments, &c., left in camp by the troops, were 1,200 rifle muskets of U. S. manufacture, late model, . 58 caliber; 6 field pieces, brass; 25 kegs of powder; from 30 to 40 horses; and several arm-chests of arms understood to be like the 1,200 muskets mentioned.

During the surrender of Camp Jackson and their passage into our lines a mob attacked our force, a published account of which will be transmitted. + The prisoners, some 50 officers and 639 men, were marched under guard to this post, previous to which Camp Jackson was taken possession of by two regiments of volunteers and two companies of regulars, under command of Captain Sweeney, who remained in possession all night, bringing the entire camp equipage and munitions of war into this arsenal this morning. To-day the prisoners were all released (with the exception of one captain, who declined this parole)--the officers on their parole of honor not to fight against the United States during this war, and the men on their oath to the same effect.

You will see by the returns of an election of brigadier-general for the volunteer brigade raised here that I have been elected to this office, which, so far as depends upon me, I have accepted, and the duties of which I am now performing under the authority of the President. This subject is submitted for such action as the Department may determine to be proper.

Since the foregoing were written I have noticed among the stores taken from Camp Jackson were parts of muskets, all separate, and apparently without ever having been put together, and were doubtless taken in this condition from the arsenal.

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*For Frost's second letter of May 10, inclosed by Lyon, see Frost to Harney, May 11.

+No such inclosure found.

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