THE CAMPAIGN AGAINST VICKSBURG—EMPLOYING THE FREEDMEN—OCCUPATION OF HOLLY SPRINGS—SHERMAN ORDERED TO MEMPHIS—SHERMAN'S MOVEMENTS DOWN THE MISSISSIPPI—VAN DORN CAPTURES HOLLY SPRINGS—COLLECTING FORAGE AND FOOD.HEADQUARTERS MOVED TO HOLLY SPRINGS—GENERAL M'CLERNAND IN COMMAND—ASSUMING COMMAND AT YOUNG'S POINT—OPERATIONS ABOVE VICKSBURG—FORTIFICATIONS ABOUT VICKSBURG—THE CANAL—LAKE PROVIDENCE—OPERATIONS AT YAZOO PASS.CHAPTER XXXI.