From Fredericksburg.
The only report received from Fredericksburg by the train last night was one to the effect that the main body of the enemy's army was moving down the Rappahannock in the direction of Port Royal, where it is conjectured they will attempt to construct their pontoon bridges, under protection of their gunboats. Beyond this single rumor, everything is represented at a stand- still, with little probability of a fight, which has been so eagerly looked for the past week. It would seem that Burnside like his predecessor, finds a little caution necessary in his operations against Richmond.