I received official confirmation of an important fact, report of which had previously reached me; that is, that there are less than 50 rounds of powder at the three forts at the mouth of this bay. Two hours of active fighting will exhaust the supply, and then the repetition of the contretemps at Hatteras is open, and Mobile is at the mercy of a naval power holding these forts and commanding the bay.

General Moore is here, and I at once advised him of the fact. He appeared surprised. New Orleans is equally destitute of powder. If it be possible I trust that these works will be supplied at once.

Pardon me for expressing the opinion that the five regiments constituting the garrison at Ship Island may be cut off whenever the enemy commanding the sea wills it. The waters of the Mississippi Sound can only be defended by guns afloat, and without them the Sip Island may be cut off whenever the enemy commanding the sea wills it. The waters of the Mississippi Sound can only be defended by guns afloat, and without them the Ship Island forces are at the mercy of the Black Republican feet. That garrison cannot command the Ship Island Pass. If it could, there are several others by which gunboats may enter. I am aware of the presumption of my opinion. A sense of duty prompts it, fort after the misfortune shall have befallen us I should reproach myself if I remained silent.

I am greatly indebted to the Government for the presence and instructions of Captain Lockett. I am doing all in my power t aid him in carrying his plans into execution.

I am, very respectfully, your obedient servant,

JOHN FORSYTH, Mayor.

NEW ORLEANS, September 17, 1861.

SECRETARY OF WAR:

Ship Island is evacuated. Two heavy frigates, two steamers, a brig, and two tenders were 8 miles off Ship Island at dark yesterday. As the last boat departed the steamers were bearing down upon the island.

D. E. TWIGGS.

MOBILE, September 17, 1861.

Honorable SECRETARY OF WAR:

I am just informed that there is very little powder at Forts Gaines and Morgan, Ala. Have but little. It is of the utmost importance that cannon powder be sent immediately to these forts.

A. B. MOORE.

RICHMOND, September 18, 1861.

His Excellency A. B. MOORE,

Governor Alabama:

Supplies of powder will be sent to the forts designated as soon as possible.

J. P. BENJAMIN,

Acting Secretary of War.

NEW ORLEANS, September 18, 1861.

SECRETARY OF WAR:

The enemy's fleet did considerable shelling yesterday at, as they supposed, a masked battery on Ship Island.

D. E. TWIGGS,

Major-General.