FOLLY ISLAND, S. C., April 28, 1863.

Lieutenant Colonel CHARLES G. HALPINE,

Assistant Adjutant-General, Dept. of the South:

COLONEL: Since my letter of the 24th instant to General Seymour, late chief of staff, I have not have not had anything of immediate importance to report.

My general ideas of the defense of this island were indicated in my conversation with Captain Hamilton and Major Duane. The re-enforcements then asked for I have again to renew the request.

The enemy has lately been enlarging his works on the south end of Morris Island. He now has several guns in position and an entrenched rifle pit; all evidently intended to prevent any moment from this island against his position.

I should desire to be informed with what view this island is to be held and against what attack we should make preparations. As things appear at present, and so long as there is a threatened movement against Charleston on the part of the naval and army force, the enemy will not probably withdraw any of his means of defense from about Charleston; but should he become convinced that he has nothing to apprehend for his stronghold he will probably bring his means to bear on the small force now on this island. It is easy for him to transport artillery to the south end of Morris Island, to which we could oppose but inadequate resistance. Under the protection of this artillery he could lay a brigade of boats and land an overwhelming force on this island. Under such circumstances it would be exceedingly difficult to embark unless protected by powerful naval batteries.

I have directed a careful survey to be made of the north end of this island. Should it be the intention of the general to hold this island permanently I think that a strong field work of the first class should be erected at the north end of the island. It should be armed with heavy rifled guns and in sufficient number to overpower any that the enemy can bring to bear from the opposite side. Such works, with the naval assistance in the Folly, will enable us to hold the island against any land force that the enemy can bring. The north end I think can with little labor be put in a complete state of defense. I request that the chief engineer (should the general commanding approve of m y idea) may be sent to confer with me, and that such works as may be deemed important may be erected under his general supervision.

I have the honor to be, colonel, yours, truly,

I. VOGDES,

Brigadier-General, Commanding.

[First indorsement.]

APRIL 30, 1863.

To be returned. Respectfully referred to Major J. C. Duane for his information and such action as he may see fit.

CHAS. G. HALPINE,

Assistant Adjutant-General.

[Second indorsement.]

If Folly Island is to be permanently occupied I would recommend that the three schooners loaded with the two 82-pounders and eight 32-pounders, James rifles, and six 30-pounder Parrotts should be ordered up there at once; that two companies of artillery accompany and take charge of the artillery. A work to be constructed across the island