This road approaches to within half a mile of the river at Camp Parapet, and a force approaching by either the river bank or the railroad would have to contend against this line of defense, which could be held for a long time by a force of 4,000 men. This line extends from the river to the swamp, and is a strong parapet with a good ditch. A belt of timber has been felled from the site of this line through to the lake, and if this line was well guarded it would be impracticable to turn the position. The only other routes of approach from the east involve water transportation, either by Lake Pontchartrain or Lake Borgne. A force might be concentrated at Madisonville and the rebel gun-boats at Mobile might run by Fort Pike or Macomb, and a landing be effected on the lake shore; this would be a very difficult and uncertain operation, and we should be able to prevent it.

The approach by Lake Borgne is still more difficult. These operations would demand the co-operation of a great naval power; the same may be said of the approach by the mouth of the Mississippi and Fort Livingston. From the west the approaches are similar in character. Should the main body of our army operate west of the Mississippi, the enemy will have enough to attend to without troubling New Orleans. The only available routes for the approach of an army by land from this direction are, first, across the Atchfalaya River above the mouth of the Courtalbeau, as at Simsport, and then down the Grossetete Bayou and the right bank of the Mississippi to Algiers; second, via Brahsear City and Thibodeaux to the bank of the Mississippi opposite Bonnet Carre, or by the Opelousas railroad, which approaches to nearly half a mile from the Mississippi at the line of defense along the Company Canal; this line must be overcome or turned by any force coming from the west. The line is a very strong one, and with Fort Banks and the gun-boats would be very difficult to take.

It is not armed, but is arranged for field or siege artillery in barbetts; it is about 1 mile form the river to the swamp. The canal is immediately in front of the line and extends through to Lake Salvador. This line can only be turned by expeditions in small boats coming through Lake Salvador and then approaching up the road along Bayou Barataria, which road reaches the Mississippi on MIllondon's plantation; or the bank of the river below New Orleans may be reached in small boats through bayous and canals near and below English Turn. Two light-draught armed boats in Lake Salvador would effectually stop any such attempts. Small boats could also be passed from Bayou La Fourche into these waters; this was the programme of the rebels last summer. They had collected a large number of skiffs with a view of surprising Fort Jackson or of establishing batteries on the bank of the Mississippi below the city, for the purpose of interrupting our communications.

I believe I have indicated all the possible ways by which the rebels alone could approach this city. War with a foreign power would complicate matters greatly. The most vulnerable point for such an enemy is Berwick Bay. In view of possible movements on our part the possession of Berwick Bay by a naval power would interfere most seriously with our operations and afford an excellent base of supplies for future operations. In view of this contingency the Board recommended the construction of a fortification at the mouth of the Atchafalaya.

The mode of defense adopted last season for this city was as fol-