The most important event of the past week was the evacuation of Harper’s Ferry on Friday last by the Confederate troops. This step had so often been predicted, and denied with, such confident assertions of the impregnable fortifications erected there and of the determination of the Confederate leaders to make it the chosen point for a desperate stand, that the first reports were received with doubts and incredulity.— Confirmatory statements, however, of the withdrawal of pickets from all points above and below the Ferry, of the burning of the railroad bridge, and the destruction of provisions they were unable to carry off, finally confirmed the evacuation. The troops left in two columns. One column going toward Winchester with the presumed intention of joining the force at Manassas Junction ; the other retreating through Loudon county toward Leesburg. Col. Stone’s column of United States troops is in that vicinity, though it is supposed on the Maryland side of the Potomac, and a collision is among the contingencies.