General Rosecrans, having now ascertained that Bragg was not retreating on Rome, but concentrating all his forces near La Fayette, behind Pigeon Mountain, where he was receiving reinforcements from Johnston and from Virginia, proceeded at once to concentrate his army. General McCook was ordered to hold Dougherty’s Gap, with two brigades, and to join General Thomas with the remainder of his command, with whom however, he did not close up till the 17th. On the arrival of General McCook’s corps, General Thomas moved down the Chickamauga, toward Gordon’s Mill. A manœuvre was now made to cover the La Fayette road to Chickamauga, but it was retarded by the narrowness of the roads and the disposition of the troops, and, during its progress, Colonel Minty became engaged with the enemy near Reed’s Bridge, and Wilder’s “Lightning Brigade” dashed into a superior force, from which they escaped by the La Fayette road. On the 11th, Minty’s cavalry and Wilder’s mounted brigade, were, after an obstinate struggle, driven by the enemy from Reed’s and Alexander’s bridges, to the Rossville road. General Thomas advanced during the night to Kelly’s House on the La Fayette road, where Baird’s division was posted. Here it was reported to him that a rebel brigade, isolated by the burning of Reed’s bridge, was on his side of the Chickamauga. Brennan, with two brigades, was sent out to capture it, and encountered a strong column of the enemy, bent on turning the left of the Union army, and on getting possession of the road between it and Chattanooga. This movement opened the combat, and on the 19th of September, 1863, was commenced. THE BATTLE OF CHICKAMAUGA. The enemy combined in heavy masses on the extreme left, and Croxton’s brigade of Brennan’s division became engaged with the rebel General Forrest’s cavalry, about ten A. M. General McCook, who had closed up to Crawfish Springs as soon as Thomas’s column was out of his way, now sent Johnson’s division to Thomas’s assistance. General Crittenden had dispatched Palmer’s for the same purpose. The support was afforded most opportunely. Croxton’s brigade, which had driven the cavalry under Forest near half a mile, met at last Ector’s and Wilson’s brigades, which made a resistance so obstinate, that Baird’s whole division was advanced to Croxton’s support. The foe was again pushed back and many prisoners captured. After an hour’s hard fighting against overwhelming numbers, the ammunition of Croxton’s brigade was exhausted, and the men were moved to the rear to enable them to fill their boxes. The united forces of Baird and Brennan had driven the enemy from their immediate front, and Baird was disposing his lines to receive an attack he had reason to apprehend on his right, when Walthall’s and Govan’s rebel brigades, under Liddell, impetuously assaulted Scribner’s and King’s, and put them to flight, making several hundred prisoners, and capturing Loomis’s and other batteries.