The port of Sebastopol consists of a bay running in a south-easterly direction, about four miles long, and a mile wide at the entrance, diminishing to 400 yards at the end, where the Tchernaya or Black River empties itself. On the southern coast of this bay are the commercial, military, and careening harbors, the quarantine harbor being outside the entrance--all these taking a southerly direction, and having deep water. The military harbor is the largest, being about a mile and a half long by 400 yards wide, and is completely land-locked on every side. Here it is that the Black Sea fleet is moored in the winter--the largest ships being able to lie with all their stores on board close to the quays. The small harbor, which contains the naval arsenal and docks, is on the eastern side of the military harbor, near the entrance. The port is defended to the south by six principal batteries and fortresses, each mounting from 50 to 190 guns; and the north by four, having from 18 to 120 pieces each; and besides these, there are many smaller batteries. The fortresses are built on the casemate principle, three of them having three tiers of guns, and a fourth two tiers. Fort St. Nicholas is the largest, and mounts about 190 guns. It is built of white limestone; a fine, sound stone, which becomes hard, and is very durable, the same material being used for all the other forts. Between every two casemates are furnaces for heating shot red hot. The calibre of the guns is eight inches, capable of throwing shells or 68-pound solid shot. Whether all the guns in the fortress are of the same size, it is impossible to say; but the belief is, that most of the fortifications of Sebastopol are heavily armed. Sebastopol is admirably adapted by nature for a strong position towards the sea, and has been fully taken advantage of to render it one of the most formidably fortified places in that direction which could be imagined. In speaking of the means of defence at Sebastopol, we have left the Russian fleet out of the question. This, however, is not to be treated either with indifference or contempt. There were in the military harbor of Sebastopol twelve line-of-battle ships, eight frigates, and seven corvettes, comprising the Black Sea fleet, independent of steamers. The town of Sebastopol is situated on the point of land between the commercial and military harbors, which rises gradually from the water’s edge to an elevation of 200 feet, and contains 31,500 inhabitants. Including the military and marines, the residents numbered 40,000. It is more than a mile in length, and its greatest width is about three-quarters of a mile--the streets entering the open steppe on the south.