strong defensive position to one of their own selection, where their greatly superior force could attack us with certainty of success. Learning in the course of the evening, from various reliable sources, that the enemy, failing in this, contemplated a flank movement — crossing the Potomac with one division above and another occupying Loudoun Heights, so as to command our naval battery and cut off our communication below Harper's Ferry, while the remaining force menaced us in front — it was determined to withdraw our troops from Bolivar Heights, and take up a second line of defence on the heights known as Camp Hill, immediately above the town of Harper's Ferry. The occupation of this inner line presented a two-fold advantage; first, that being much less extended, it could be held by a smaller force, the enemy, from the nature of the ground, being unable to bring into action a larger force than our own; secondly, that it would enable us to bring our naval battery on the Maryland Heights to bear upon the enemy as they advanced down the declivity of Bolivar Heights into the valley which separates it from Camp Hill. They would thus be exposed for a considerable time to a heavy fire from this formidable battery, where great elevation would enable it to throw shells directly over the heads of our own forces on Camp Hill into the faces of the advancing foe. With the force rendered by this contraction of our front available for other purposes, it was deemed prudent to occupy the crest of the hill, above the naval battery on the Maryland shore, to frustrate any attempt of the enemy to take this hill in the rear and turn our batteries against us. The movement having been decided upon, orders were immediately given for its prompt execution. This was about midnight. Gen. Cooper's brigade was at once set in motion, and by daylight had succeeded in crossing the river and occupying the heights on the Maryland side. Gen. Slough's brigade at the same time fell back to the new position on Camp Hill, and when morning dawned our batteries, (companies K and L, of the First New-York artillery,) supported by a heavy force of infantry, were in position to command all the approaches on our front and flanks; the remainder of the infantry being posted as reserves along the brow of the hill, under cover of the town and houses. The weak portions of this line were subsequently strengthened by breastworks hastily erected. On Friday morning Major Gardner, with the Fifth New-York cavalry, was sent to the front to feel the enemy's position and watch his movements. He was later in the day reenforced by a piece of artiilery and two Hundred sharp-shooters. The enemy opened upon him with a scattered fire of musketry along his whole front. The first fire of grape from our piece caused the enemy's skirmishers to fall back in disorder. He then brought six pieces of artillery into action. Major Gardner, having most gallantly accomplished the object of his expedition, retired. The enemy now advanced with his artillery and shelled our former position on Bolivar Heights. Having done this, he withdrew. Jackson, the commander of the rebel forces, having given the order to his army to storm our position, they advanced beyond Bolivar Heights in force to attack us, about dark on Friday evening, in the storm. Gen. Slough opened upon them from Camp Hill with Crounse's and part of Reynolds's battery, and Lieut. Daniels, from battery Stanton, on Maryland Heights. The scene at this time was very impressive. The night was intensely dark; the hills around were alive with the signal lights of the enemy; the rain descended in torrents; vivid flashes of lightning illumined at intervals the green but magnificent scenery, while the crash of thunder echoing among the mountains, drowned into comparative insignificance the roar of our artillery. After an action of about one hour's duration, the enemy retired. He made another unsuccessful attack at midnight with regiments of Mississippi and Louisiana infantry, and after a short engagement disappeared. Signal-lights continued to be seen in every direction. On Saturday morning, ignorant of the enemy's movements, I sent out a reconnoissance in force to discover his whereabouts, and found that he had retreated. I pushed forward as far as Charlestown, and found the enemy's rear-guard had left an hour before; fifty pieces of his cannon passed through Charlestown that morning. The enemy being in strong force, variously estimated at from eighteen thousand to twenty-five thousand, and many reports in circulation that he had repulsed our forces sent to attack him in the rear, and my own force of not more than seven thousand effective men being completely worn out by fatigue and exposure, I deemed it not prudent to advance, at least until they were rested. On Sunday Gen. Sigel arrived, and on Monday he assumed the command. I have not yet received the reports of the subordinate commanders, and cannot particularize individual instances of good conduct. As a general thing, the troops bore their fatigue and hardships with cheerfulness. Great credit is due to Brigadier-Generals Cooper and Slough, commanding the First and Second brigades respectively, for their untiring exertions during the five days and nights' siege. Also, to Col. D. S. Miles, commanding the railroad brigade, and his aids, Lieuts. Binney and Reynolds, as well as to my own personal staff, Capt. George Merrill, Assistant Adjutant-General; Capt. J. C. Anderson and U. Dahlgren, additional aids-decamp; Major George W. Bruin, volunteer aid, and Mr. Thorndyke, of the Eighth Missouri regiment, who volunteered his services on this occasion. Lieut. Daniels, with his naval battery of Dahlgren guns on Maryland Heights, two thousand feet above the level of the sea, did splendid service throughout the entire siege. Very respectfully, your obed't serv't,
R. Saxton, Brigadier-General United States Volunteers.