In order to understand the nature of the reconnoissance, it will be necessary to have a clear apprehension of the geography of the country. Savannah is about fifteen miles from the mouth of the river, and on the right or southern bank. Approach to it by water is defended by Fort Pulaski, a casemated fort on Cockspur Island, at the mouth of the river, and Fort Jackson, a barbette fort on the mainland, only four miles below the city. The left bank is formed by a succession of islands, and the channel also is interrupted by large and numerous islands, the most important of which is Elba, whose upper extremity is immediately opposite Fort Jackson. Lower down in the stream is Long Island. The network of creeks and bays that surrounds Hilton Head terminates southward in Calibogue sound, which is divided from the Savannah river at its mouth by Turtle and Jones Island. The waters that form two sides of Jones Island, which is triangular in shape, are called Mud and Wright rivers; the latter is the southernmost, and separates Jones from Turtle Island, which lies next to Dawfuskie Island, the western shore of Calibogue sound. The islands on the Savannah are all very low and marshy, overgrown by high grass, and frequently without a solitary shrub or tree; they are all liable to be submerged by a very high tide. Jones Island is a broad, marshy, uninhabited island, five miles above the fort, not more than five miles long, by two or three broad. About half way between its upper and lower angles, and fronting on the Savannah, is Venus Point. This first reconnoissance was undertaken by Lieutenant J. H. Wilson, of the topographical engineers. Taking with him two boats and a company of Rhode Island soldiers, together with his negro oarsmen and pilots, he started on the dangerous expedition, making all the necessary explorations by night, while his boats were hidden by the tall grass on the marshy and swampy shores he traversed. To the rear of Jones Island he discovered a canal called Wall’s Cut, connecting the Mud and Wright rivers, the former emptying into the Savannah six, and the latter two miles above Fort Pulaski. The navigation of Wall’s Cut had been obstructed by three rows of piles, driven across its entire width by the rebels, but at high tide the boats were got over these obstructions, and soon after floated on the waters of the Savannah, at night, unobserved by the rebels. The feasibility of traversing this route with the gunboats had been demonstrated, but the movement was betrayed to the rebels before the plan could be consummated.