morning, the bridge should be finished in three hours, and at night the detachment should be in position on the Bowling Green and Fredericksburg road and watching the Telegraph road. At Franklin's crossing the bridges should be ready at 8 a. m. Cavalry, with two or three brigades of infantry to clear the way, should cross at United States Ford or at Banks' Ford, if possible, and act on the enemy's flank and rear. If it were deemed impracticable for the cavalry to force a passage at these points, as they would have a long detour to make, they should start the preceding day. In case of the crossings mentioned, the enemy would seem to have three courses to follow - first, to fall back at once; second, to send a detachment to meet ours toward Port Royal and to fight us at Franklin's crossing; third, to leave a rear guard at Franklin's crossing and throw his main force on our detachment near Port Royal. In the first case both our main body and detachment should follow at once; in the other two, both main body and detachments should attack as soon as they are in presence of the enemy. The cavalry should be prepared for the possibility of the enemy's falling back toward Gordonsville. It would seem that nothing decisive would be effected by crossing the army at Banks' or United States Ford. The crossing would be on the enemy's left flank and he could not concentrate rapidly, but, on the other hand, if he fell back we should be seven or fifteen miles from his central masses when across the river. Prisoners have stated that when the attempt was made to cross at Banks' Ford very few of the enemy's troops were moved up, as they did not believe we could cross there. May not the true reason have been that they intended to fall back if we crossed and proposed only to resist the building of the bridges?

C. B. COMSTOCK,

Captain and Engineers and Chief Engineer Army of the Potomac.

(Handed General Hooker April 12.)

[25.]

HEADQUARTERS FOURTH ARMY CORPS,
Fort Yorktown, Va., April 12, 1863.

Major WILLIAM P. HALL,

Commanding Sixth New York Cavalry:

MAJOR: As Colonel West may be attacked in force at Fort Magruder at any time and your and our communication with him be cut off, the commanding general desires you to be governed by the following instructions until further orders: You will keep yourself constantly advised of the movements on the front, patrolling the country well to your front and flanks to detect any attempt of the enemy to get to the rear of Fort Magruder. In case you find your communication with Colonel West cut off, you will report the fact at once to these headquarters. Captain Paul will then be ordered to report at once to you, and d thus strengthened you will exercise the utmost care and vigilance in watching the enemy's movements. You will not retire to this fort until actually compelled to do so to insure the safety of your command, but will constantly patrol the roads and country generally, and will make frequent reports to these headquarters of everything that occurs.

Very respectfully, your obedient servant,

C. C. SUYDAM,

Assistant Adjutant-General.

[18.]