Mobile to be Attacked.
--We learn from a gentleman just from New Orleans (says the Mobile Tribune, of the 25th,) that on the 11th instant about 20,000 of Grant's army landed at Camp Parapet, which is about three miles above Carrolton. It was stated by the Yankees that within a day or two 10,000 more would arrive. These men stated that they would either rendezvous at Ship Island or Pensacola, and they intended to take Mobile within six weeks.