Bankhead reports 4 feet water at low tide around Cunningham Point. A shot from Fort Pulaski fell within 30 yards of his launch while sounding. Captain Bankhead also informed me that he saw very plainly this morning at 11 o'clock two steamers towing a large wreck into Saint Augustine Creek. This, with the piles reported to have been encountered by Captain Davis (as Bankhead informs me), locks like a very serious obstacle in Saint Augustine Creek. I learn that our gunboats have all left there. No boats have passed to or from Pulaski to-day. One went down and back last night. No guns have yet been put in battery at the Cut. Captain Hamilton thinks that two 30-pounder Parrots can be towed down early to-morrow morning. If deemed necessary they will be put in position. I look anxiously for additional light-draught gunboats, something that can through on 9 feet water.

If the Wright River route turns out to be impracticable (or decided to be so I believe our lightest-draught gunboats can go down Mud River on a high tide, and (without going into the Savannah) can cover our erection of batteries on Jones Island. I also think, from what the contrabands say, that a side-wheel steamer running up and down Mud River will depend the channel very much. The bottom is very soft; a 10-pound lead sinks 1 1/2 feet into the mud. Suppose we try this plan: Failing in all these plans I propose to built a dike causeway across the lower or the upper end of Jones Island (from Wright or Mud River) and carry our guns across to venus Point. This os of course a denier reassort. The alternative may ne to take our flats into Savannah River without protection. Lieutenant O'Rorke and Major Beard are now out, with instructions to examine the upper end of Long Island and the lower end of Elba. To-morrow morning I shall go down Wright River to examine Jones Island at the lower end up to the beacon. I could not approach it from the upper end on account of a creek, as I stated last eve.

Very respectfully, your obedient servant,

Q. A. GILLMORE,

Captain and Chief Engineer.

P. S.- My command is now engaged in making fascines and gabious.

[Inclosure Numbers 6.]

DAUFUSKIE ISLAND, S. C., Jan. 30, 1862 - 7.30 p. m.

Brigadier General THOMAS W. SHERMAN,

Commanding Expeditionary Corps, Hilton Head, S. C.:

SIR: I have to report the safe return of Lieutenant O'Rorke (accompanied by Major Beard) from an examination of Long Island and Elba Island. I inclose a memorandum furnished by Lieutenant O'Rorke in advance of his report. The position near the upper end of Long Island is favorable for the erection of a battery should one there be deemed necessary or advisable.

In my report of last evening I suggested the expeditionary of building a causeway to Venus Point (if a battery be put there, connecting with Mud or Wright River. I have caused the line running from Venus Point due north to Mud River to be examined to-day. A causeway can be easily constructed over that line. The line to Wright River will be examined to-morrow morning. Even if the Navy cover our erection of batteries on Venus Point, we want a line of communication with the rear other than by water through Mud or Wright Rivers, inasmuch as we might lose the control of the mouths of these streams in the absence