Report of a conference in relation to the occupation of points on the Atlantic coast.

WASHINGTON, D. C., July 13, 1861.

Honorable GIDEAON WELLES,

Secretary of the Navy:

SIR: We have the honor to inform you, in further prosecution of the duties assigned us, we have made a careful study of three of the most important of the secondary bays or harbors on the Southern coast, for the purpose of military occupation. These are Bull's Bay, Saint Helena Sount, and Port Royal Sound, all on the coast of South Carolina. We shall describe each one of them separately, offering some suggestions as to their advantages and the best mode of occupying them, and we will endeavor to explain, by a comparison of their relative mertis, the grounds for preferring the two former over the latter for immediate occupation. We have taken them up in the order of their situation from north to south.

Bull's Bay, which has been justly called Noble Harbor of Refuge, is fifteen miles southwest of Cape Romain and twenty-two miles from the main bar of Charleston Harbor. The passage into it is direct, there being but one single course over the bar. The light-house is plainly in sight, being less than four miles distant from the outer curve of the bar, and its bearing, together with the soundings and buoys, when properly placed, makes the entrance easy. Twenty feet may be carried in at high water of common tide and fifteen at low water. The channel-way is marked by breakers on either hand, and inside there is a snug, well-protected anchorage in deep water, with good holding-ground. Bull's Bay is situated below the parallel at which the West India hurricanes leave the coast, which very much increases its value as a harbor of refuge. Bull's Island, from which the bay takes its name, is six miles and a half long and about one mile and a half wide. The northeast bluff at the entrance is high and wooded, and admits of being strongly fortified without delay or great expense; but batteries erected to defend the entrance may be taken in the rear by landing about three miles south of the northeast bluff, and keeping on the beach till within a mile of the light-house, where of sand hills commanding the entrance. It is suggested, therefore, that the extremity of the island should be secured by an inclosed work on the point and a line of intrenchments across the island at a distance of two miles, more or less, from the light-house. For defense, Bull's Bay possesses this striking advantage, that it can be held at a single point. Excepting the small sand key (Bird Island), there is no fast land from which it can be attacked. Bird Island is two miles off, not easy of access, and insignificant.

It is not probable that any defensive works constructed by the rebels will oppose any formidable obstacle to the occupation of the place, but it is to be considered that its proximity to Charleston subjects it to assault. This assault may be made by combined forces from both directions, for there is interior water communication with the Santee on the north, as well as with Charleston on the south. Vessels drawing not more than four and a half feet can come out of the Santee through Alligator Creek at the Horns, pass within Cape Island and Raccoon Key, traverse Bull's Bay, and keep inside all the way to Charleston. Very few white men know the whole route, but many negroes are familiar with it. There are six "divides", or places where the tides diverge or converge, between Cape Romain and Charleston Harbor.