JACKSON, January 25, 1863.

Major-General GRANT,

Memphis:

A son of McWilliams has just arrived from Mobile. He reports the city as being strongly fortified, and General Buckner in command, with 20,000 troops. The Mobile and Ohio Railroad is run no farther north than Okolona, where there are 2,000 cavalry. Mobile is protected on north side by a triple line of works, a distance of 3 miles from the city. The harbor is driven full of piles, leaving a winding channel commanded by heavy guns. This channel is so narrow that a heavy steamer, which ran the blockade, was unable to reach the city. He understands that no cars run as regular trains higher than Jackson. The boy is about fourteen years old.

JER. C. SULLIVAN,

Brigadier-General, Commanding.

HEADQUARTERS ARMY OF THE Mississippi,
Near Vicksburg, January 26, 1863.

Major General U. S. GRANT,

Comdg. Dept. of the Tennessee:

I have only to add to my dispatch of the 24th instant that the Mississippi River is still rising; that three crevasses occur within 20 miles of the lower end of the canal, and that the country for some 12 miles above New Carthage is being rapidly overflowed. The first of this series of crevasses occurs about 3 miles below the canal, and about 1 mile below my left wing; the SECOND, 4 miles below the first, and the THIRD, 10 miles below the SECOND.

Two others occur in front of my right wing, and demand the indefatigable labor of details, with the few implements I have, to mend them. Thus the implements are needed not only for the purpose of cutting the canal, but to avert the necessity of leaving here until sheer necessity may compel it. With the threatened danger of a flood before me, I am confirmed in my determination to retain enough transports here to remove my command, if forced to that dire necessity.

The water flows 3 feet deep in the canal, but gives no evidence of diverting the channel of the river. I have ordered all the men I can employ with the limited number of implements available to make a lateral cut from the main trunk terminating higher up the river. These men worked all last night and to-day.

I am doubtful that even this change will prove successful, but as it will cost but comparatively little time and labor, I thought I would try it.

I am causing such examinations and surveys as present necessities and flooded sloughs, bayous, and marshes will permit, contingently with a view of cutting a canal higher up the river.

I compassed the front of my right wing to-day, passing from the river to the railroad, and found 3 flat cars and 28 trucks on the track. The coast on the WEST bank of the river for 20 miles below Vicksburg, as well as on both banks above, to Memphis, has been abandoned by almost all proprietors, who have retired from this vicinity, with their movables and negroes, to Monroe [La.]. In many cases they have left foreigners, chiefly Irishmen, behind to take care of their houses.

Having received no confirmation of a report, two days old, that General Banks had taken Port Hudson, I am not authorized to accept it as true.