From the Southwest.
Mobile July 26th
--A special dispatch to the Advertiser, dated Chattanooga, 25th, says: ‘"The enemy is evincing great activity, and is evidently preparing for some movement.
Trains of cars arrived at Bridgeport to-day, with shell and ammunition.
Some rumors which have been circulating, respecting the retreat of the enemy, are ascertained to be false."’
A special dispatch to the Tribune, from Grenada, 25th, says: ‘"Memphis refugees report that a portion of Sherman's army left that city on Tuesday last for the Lower Mississippi--supposed to be for Vicksburg."’
Two disabled Yankee gunboats, towed by steamers, passed Helena, on Monday, upward bound.
Six Federal Colonels, it is said, have resigned in Curtis's army, owing to Lincoln's late policy on the negro question.
Many other officers have resigned at Memphis and gone North.
Information; deemed reliable, has been received here that Gen. Curtis hung three of our guerrillas at Helena.
He has again moved all his force to the other side of the river. 