From the Southwest.
Demopolis, March 17.
--A dispatch from Canton reports that a large number of Sherman's troops have gone up the river on furlough from Vicksburg.
McPherson is left in command of that place.
Sherman and Hurl but have gone down the river with a large part of the army on forty-two boats.
They are said to be going up Red river to Shreveport.--McPherson reports the spring campaign, which was inaugurated by Sherman, Banks, Thomas, and Smith, a failure.
Gen. Forrest says that seven- eights of Smith's cavalry have gone to Nashville.
Another dispatch says that Sherman went to New Orleans, and returned to Vicksburg on the 5th.
On the 6th inst. large numbers of re-enlisted men went up the river on furlough.
From fifteen to twenty boat loads of troops came down the river up to the 9th or 10th.
On the 1st inst. seven boat loads of troops are said to have gone up the river on furlough.
One-third were left in Vicksburg, under McPherson, and the remainder have gone up Red river. 