September 20.

Lee, on receiving Pendleton’s report, long after midnight, sent off orders for Jackson to drive the enemy back.  When the messenger arrived, Jackson had already ridden to the front.  He, too, had received news of the capture of the guns; and ordering A.P.  Hill and Early,* (* Commanding Ewell’s division, vice Lawton, wounded at Sharpsburg.) who were in camp near Martinsburg, to march at once to Shepherdstown, he had gone forward to reconnoitre the enemy’s movements.  When Lee’s courier found him he was on the Shepherdstown road, awaiting the arrival of his divisions, and watching, unattended by a single aide-de-camp, the advance of Porter’s infantry.  He had at once grasped the situation.  The Confederates were in no condition to resist an attack in force.  The army was not concentrated.  The cavalry was absent.  No reconnaissance had been made either of lines of march or of positions.  The roads were still blocked by the trains.  The men were exhausted by their late exertions, and depressed by their retreat, and the straggling was terrible.  The only chance of safety lay in driving back the enemy’s advanced guard across the river before it could be reinforced; and the chance was seized without an instant’s hesitation.

The Federals advanced leisurely, for the cavalry which should have led the way had received its orders too late to reach the rendezvous at the appointed hour, and the infantry, compelled to reconnoitre for itself, made slow progress.  Porter’s leading brigade was consequently not more than a mile and a half from the river when the Light Division reported to Jackson.  Hill was ordered to form his troops in two lines, and with Early in close support to move at once to the attack.  The Federals, confronted by a large force, and with no further object than to ascertain the whereabouts of the Confederate army, made no attempt to hold their ground.  Their left and centre, composed mainly of regulars, withdrew in good order.  The right, hampered by broken country, was slow to move; and Hill’s soldiers, who had done much at Sharpsburg with but little loss, were confident of victory.  The Federal artillery beyond the river included many of their heavy batteries, and when the long lines of the Southerners appeared in the open, they were met by a storm of shells.  But without a check, even to close the gaps in the ranks, or to give time to the batteries to reply to the enemy’s fire, the Light Division pressed forward to the charge.  The conflict was short.  The Northern regulars had already passed the ford, and only a brigade of volunteers was left on the southern bank.  Bringing up his reserve regiment, the Federal general made a vain effort to prolong his front.  Hill answered by calling up a brigade from his second line; and then, outnumbered and outflanked, the enemy was driven down the bluffs and across the river.  The losses in this affair were comparatively small.  The Federals reported 340 killed and wounded, and of these a raw regiment, armed with condemned Enfield rifles, accounted for no less than 240.  Hill’s casualties were 271.  Yet the engagement was not without importance.  Jackson’s quick action and resolute advance convinced the enemy that the Confederates were still dangerous; and McClellan, disturbed by Stuart’s threat against his rear, abandoned all idea of crossing the Potomac in pursuit of Lee.