Orleans this week. Two tons of saltpeter were ordered from Augusta to New Orleans on the 19th instant.

J. P. BENJAMIN,

Acting Secretary of War.

NEW ORLEANS, September 23, 1861.

SECRETARY OF WAR:

I have countermanded the movement of the Third Regiment to General Polk at the wish and with the concurrence of Governor Moore.

D. E. TWIGGS.

ENGINEER BUREAU,

Richmond, Va., September 23, 1861.

Honorable SECRETARY OF WAR:

SIR: The defensive works for the protection of Mobile Bay and city consist of Forts Morgan and Gaines, a battery at Grant's Pass, and other batteries now under construction in the immediate neighborhood of the city. Fort Morgan has five 10-inch columbiads, two of them known to be mounted; two others probably so; the fifth on the way, not arrived. Some ten other heavy guns (rifled) and columbiads ordered by Mr. Secretary Walker are anxiously expected, and are believed to be under fabrication in this city. There are also but thirty-eight 32-pounders mounted on the work, which are now being rifled. From these last we cannot expect the full range and power of guns made of rifling, but when the full armament shall have been received it will be formidable. Two redoubts are under construction on the land side in advance of Fort Morgan. Present garrison, one regiment:

Fort Gaines is opposite Fort Morgan, 3 1/4 miles distant, and the two are required to protect the intervening channel. This work was intended to mount one columbiad in each bastion (five of them) and fifty 32-pounders in barbette on the curtains. It has two 10-inch columbiads, probably not yet mounted, as their carriages (new iron) do not fit the old and usual form of traverse circle. The alteration is being made. Two rifled guns and one 8-inch smooth bore are required there, and will be mae in this city. Ten 32-pounders are mounted on the curtains. Four of its flanking guns have been received, and are probably mounted. Sixteen more of the last-named guns (howitzers) are required, and are being made at Florence, Ala. The present garrison of Fort Gaines is supposed to be three companies.

Fort Morgan and Fort Gines are permanent works, with walls of brick masonry. The battery at Grant's Pass mounts three 32-pounders, which will soon be rifled; garrison, one company. Near the city, in the neighborhood of Choctaw Pass, a battery is being built in the water to command the channel in case small vessels should run past the forts or armed launches be hauled across the peninsula of Mobile Point. Some batteries are being thrown up on the land front of the city, for which guns were ordered by Mr. Secretary Walker. The labor for this last work is understood to be furnished gratuitously by the citizens.

The great want of Mobile Bay is armed steamer, to cope with any armed small craft which might steal into the bay at night or be hauled over land, as already mentioned. A single armed launch could cut off communication between the city and the forts, for there is literally nothing in which to make head against such an invader. A steamer