No advance was made by the Federal forces on the 18th, which passed away without any engagement. General McClellan was waiting for reinforcements under Generals Couch and Humphreys, then on their way, and in the mean time, had ordered an attack on the 19th. A reconnoissance of the Federal cavalry advanced to the Maryland shore of the Potomac on the evening of the 19th, where they skirmished with the rear guard of the rebels, and captured six guns. General Lee had safely withdrawn his army to the Virginia shore, and was slowly conducting his retreat to the banks of the Rappahannock. Though the battle of Antietam can hardly be classed as a decisive victory on the part of the Federal forces, in a strictly military point of view, it was conclusive in its results; and General Lee retreated into Virginia with a full conviction of his inability to cope successfully on that ground with the army opposed to him, and thoroughly dispossessed of the confident expectation he had entertained, that the inhabitants would flock by thousands to his standard, when his forces should appear in their midst. Restricted as he had ever been in his commissariat, he had discovered that no dependence could be placed on obtaining supplies in a hostile territory, surrounded by a numerous and vigilant foe, whose well-disciplined and eager cavalry would surely cut off any supplies from the Shenandoah Valley, long before they reached the banks of the Potomac. With a loss of thirty thousand men, in killed, wounded and prisoners, he was compelled therefore to retrace his steps, which he was allowed to do, deliberately and securely. M’CLELLAN’S ARMY ON THE POTOMAC. OCTOBER 1–26, 1862. At this juncture in military affairs, the cautious policy of General McClellan once more came into conflict with that of the United States Government, at Washington. It was McClellan’s desire to reorganize the army, which had suffered much under the command of General Pope, and which had just passed through two severe battles. Maryland Heights and Harper’s Ferry had been occupied and fortified, and, as the Potomac was low, and easily fordable by rebel raiders, McClellan designed to stretch his forces along that river, from near Washington, to Cumberland, a distance of about one hundred and fifty miles, to prevent further incursions, and to make occasional sallies for reconnaissance or offensive operations, while the work of reorganization should be in progress. General Halleck, on the other hand, representing the President and the War Department, denied the necessity for any delay and urged an immediate onset.