It was on the 30th of July that McCausland burned Chambersburg. In the confusion caused by his rapid movements, Halleck imagined that Early's whole force was in Pennsylvania. Therefore he ordered Wright back into Maryland, first to Frederick and them to Emmettsburg, to hold the passes of the South Mountain against the supposed invader. About noon Wright faced about, taking Crook with him, and recrossed the Potomac. Toward evening Crook and Wright covered the passes, while Emory crossed the Catoctin and at one in the morning of the 31st halted near Jefferson after a hard day's march of thirteen miles, during which the men and animals of all the corps suffered terribly from the heat and dust, added to the accumulated fatigue they had already undergone from a succession of long days and short nights. Reveille was sounded at five o'clock, and at six the march was resumed. Emory passed through Frederick, moved about two miles on the Emmettsburg road and went into bivouac, having made thirteen miles during the day. The army was now concentrated at Frederick, holding the line of the Monocacy and observing the passes of the South Mountain. Fortunately for the men and horses, Halleck now learned from Couch, who commanded in Pennsylvania, with rather less than a handful of troops, the exact dimensions of McCausland's raid. Accordingly Wright's troops were allowed to rest where they were. Grant ordered up a division of cavalry from the Army of the Potomac, and on the 4th of August set out in person for Frederick, avoiding Washington, to see for himself just what the situation was, and to make better arrangements for the future. On the 5th of August he joined Hunter on the Monocacy, and at once ordered him to take Wright, Emory, and Crook across the Potomac, to find the enemy, and to attack him. Grover's division and the parts of Emory's that had been at Bermuda Hundred embarked on the James on the 31st of July, and passed up the Potomac to Washington, but too late to join Emory on the Monocacy. Thus, before beginning the new movement, Emory had of his own division 4,600 effective and eight regiments of Grover's, numbering 2,750. These, being part of four brigades, were temporarily organized into two, and as Grover himself had not yet joined, their command was given to Molineux. About this time, Battery L, 1st Ohio, was relieved from duty with the Nineteenth Corps, and four other batteries joined it from the reserve park at Washington. Of these Taft's 5th New York was assigned to the First division, Bradbury's 1st Maine, an old friend, to the Second division, Lieutenant Chase's D, 1st Rhode Island and Miner's 17th Indiana to the Artillery Reserve, commanded at first by Captain Taft, afterward by Major Bradbury.