We shall watch with the greatest anxiety the movements of yourself and General Grant. I have urged him to keep his forces concentrated as much as possible, and not to move east till he gets control of the Mississippi River.

Very respectfully, your obedient servant,

H. W. HALLECK,

General-in-Chief.

HDQRS. DEPT. OF THE GULF, NINETEENTH ARMY CORPS,
Sims' Plantation, opposite Simsport, May 19, 1863-8 p.m.

Major General N. P. BANKS,

Commanding Department:

GENERAL: I have the honor to report as follows: Lieutenant [Franklin] Harwood reports from Morganza that the road along the river to that place is practicable for all arms. About 200 of the enemy' cavalry were in his front yesterday, but none to be seen to-day; they signaled along his front. A paroled soldier reported to him that there were only 2,000 men in Port Hudson. Commodore Palmer says that a dispatch from Admiral Porter states that the enemy are said to be evacuating Vicksburg.

Intercepted letters from Mobile show that there is but a small force there. Everything appears to have been sent to re-enforce Johnston in front of Rosecrans. An intercepted letter from a captain in the rebel army, under Johnston, represents his force at about 55,000 men, date April 16. Another intercepted letter from Richmond, date April 8, states that there are at least 50,000 men in that army; this letter is written by H. L. Clay, who appears to be connected with the office of the rebel Adjutant-General. He further intimates that the question of subsistence is the doubtful one with them. The letter is directed to Dr. S. A. Smith, Alexandria.

Several of the letters recently found in the intercepted mails are of considerable importance. One of them refers to the construction in England of iron-clads for the Emperor of China, and states that one of them is to be commanded by an officer whom he names, and who is certainly not a Chinaman. Both Grover's and Emory's divisions and most of their trains are now on this side. We are well supplied with ammunition, and have about twenty-five days' rations (partial rations) on hand. We shall need forage for the horses, this section of the country appearing to be pretty well stripped. Major Carpenter has applied to have some sent up, but I believe forage is rather short at Brashear. I propose to send down to Brashear to-morrow the Laurel Hill, and probably the Empire Parish, with the Sixth New York Regiment, which is to be sent to New York to be mustered out, and a load of prisoners, sick, contrabands, and mules, &c., getting rid of as much impedimenta as possible. Dr. Bacon is on the Laurel Hill. The raft is not here yet, but the Estrella has gone for it.

The rebels are evidently massing their western forces against Rosecrans, and very wisely, too. Grant should at once re-enforce Rosecrans to the utmost, leaving only enough before Vicksburg to mask its garrison. We should take Port Hudson and then re-enforce Grant before Vicksburg, enabling him still further to re-enforce Rosecrans. This should doubtless have been arranged earlier, but it is not too late to give Rosecrans the superiority in time, a t least, to prevent serious disaster. I hope the Government appreciates the importance of Rosecrans'