rest of the army should be within supporting distance, and Longstreet and Hill marched to the Potomac. The former crossed at Williamsport and the latter at Shepherstown . The column reunited at Hagerstown, and advanced thence into Pennsylvania, encamping near Chambersburg on the 27th. No report had been received that the Federal Army had crossed the Potomac, and the absence of the cavalry rendered it impossible to obtain accurate information. IN order, however, to retain it on the east side of the mountains, after it should enter Maryland, and thus leave open our communication with the Potomac through Hagerstown and Williamsport, General Ewell had been instructed to send a division eastward from Chambersburg to cross the South Mountain . Early's division was detached for this purpose, and proceeded as far east as York, while the remainder of the corps proceeded to Carlisle . General Imboden, in pursuance of the instructions previously referred to, had been actively engaged on the left of general Ewell during the progress of the latter into Maryland . He had driven off the forces guarding the baltimore and Ohio Railroad, destroying all the important bridges on that route from Cumberland to Martinsburg, and seriously damaged the Chesapeake and Ohio Canal. He subsequently took position at Hancock, and after the arrival of Longstreet and Hill at Chambersburg, was directed to march by way of McConnellsburg to that place . Preparations were now made to advance upon Harrisburg ; but, on the night of the 28th, information was received from a scout that the Federal Army, having crossed the Potomac, was advancing northward, and that the head of the column had reached the South Mountain. As our communicate with the Potomac were thus menaced, it was resolved to prevent his farther progress in that direction by concentrating our army on the east of the mountains. Accordingly, Longstreet and Hill were directed to proceed from Chambersburg to Gettysburg, to which point General Ewell was also instructed to march from Carlisle. general Stuart continued to follow the movements of the Federal Army south of the Potomac, after our own had entered Maryland, and. in his efforts to impede its progress, advanced as far eastward as Fairfax Court-House . Finding himself unable to delay the enemy materially, he crossed the river at Seneca, and marched through Westminster to Carlisle, where we arrived after General Ewell had left for Gettysburg . By the route he pursued, the Federal Army was interposed between hi command and our main body, preventing amy communication with him hi arrival at Carlisle . The march toward Gettysburg was conducted more slowly than it would have been at the movements of the Federal Army been known. The leading division of Hill met the enemy in advance of Gettysburg on the morning of July 1. Driving back these troops to within a short distance of the own, he there encountered a larger force, with which two of his division became engaged . Ewell, coming up with two of his division by the Heidlesburg road, joined in the engagement . The enemy was driven through Gettysburg with heavy loss, including about 5, 000 prisoners and several pieces of artillery . He retired to a high range of hills south and east of the town . The attack was not pressed that afternoon, the enemy's force being unknown, and it being considered advisable to await the arrival of the rest of our troops . Orders were sent back t hasten their march, and,