ENGINEER BUREAU,

Richmond, March 12, 1862.

Honorable J. P. BENJAMIN, Secretary of War:

SIR: The following report is respectfully submitted as a partial reply to the resolution of Congress of the 24th February, calling for information, surveys, and reports connected with the defense of Richmond:

In ascending the James River the defenses consist of-

1st Fort Boykin, Day's Neck.- Mounting ten guns; 42-pounders and 32-pounders, hot shot, &c.

2nd Fort Huger, Harden's Bluff.- Mounting thirteen guns; one 10-inch columbiad, pattern rifled, en barbette, four 9-inch Dahlgrens en barbette, two 8-inch columbiads en barbette, six hot-shot 32-pounders on ship carriages.

3rd. Mulberry Island Point Battery.- Five 42-pounder guns en barbette, two 8-inch columbiads en route, fifteen casemates building rapidly, and large covering work nearly completed.

4th. Jamestown Island Batteries.- Thirteen guns; four 9-inch Dahlgrens, four 8-inch columbiads and two more en route, five hot-shot long 32s.

5th. Drewry's Bluff Battery, coupled with obstructions in the river, is being rapidly constructed, under the direction of Lieutenant Mason, of the Provisional Engineer Corps.

The first is completed, while the second and third are being rapidly and intelligently improved with bomb-proofs, &c., by Captain Clarke, of the Provisional Corps, who has a force of at least 1,000 hands.

From 20 to 30 miles below City Point there are two positions - Fort Powhatan and Kennon's marshes - which have been thoroughly examined by the ablest officers at the disposition of the department, and reported to be good locations for batteries. If they are placed at either of the above points obstacles should be constructed in connection with them. The final and intelligent selection of a site can consequently not be determined except by a thorough hydrographic survey.

In regard to the Richmond defenses, it was the opinion of General Leadbetter that the works around the city were rather near, but so much had been done at the time he took charge of them, that he directed me, on leaving for Tennessee, to carry out the plans adopted by the Engineer Department of Virginia. This I have sought to do with the means at my disposition, and a large proportion of the leading works are completed. Intermediate secondary breastworks could be thrown up with sufficient rapidity by the troops who are to defend the main works when there is occasion. Labor of the works are closed, and those which are not so can be rapidly protected. Directions have been given to drain the magazines thoroughly, and if necessary to construct new ones.

There are but few guns mounted on the works. A full armament for them would be exceedingly difficult to procure, and the propriety of concentrating so many pieces on a contracted local defense would seem at least doubtful.

The batteries on the Manchester hills are very nearly, if not entirely, constructed, and a force has been called out to repair and complete them. Drewry's Bluff, a most commanding point where the James River is narrowest, about 7 miles below Richmond, has been selected as the best point for a battery coupled with obstructions. In its in-