At six P.M. the pontoon-bridge was begun, under charge of Capt. Comstock of the engineers, by a detail mostly from the Eleventh Corps. Some four hundred men of Buschbeck's brigade crossed in boats, and attacked the enemy's pickets, which retired after firing a single shot. About ten P.M. the bridge was finished, and the troops crossed; the Eleventh Corps during the night, and the Twelfth Corps next morning. The Seventeenth Pennsylvania Cavalry Regiment was sent out as flankers to prevent the Confederate scouting-parties from annoying the column. In this they failed of entire success; as the rear of the Eleventh Corps was, during the day, shelled by a Confederate battery belonging to Stuart's horse artillery, and the Twelfth Corps had some slight skirmishing in its front with cavalry detachments from the same command. As soon as Hooker had seen to the execution of his first orders, he transferred his headquarters to Morrisville, five miles north of Kelley's Ford, and superintended the execution of the crossing and advance. Urging Meade to equal celerity and secrecy in uncovering United-States Ford, he instructed Slocum, should Meade's crossing at Ely's be resisted, to push a column on the south side of the Rapidan to open the latter ford. At Germania Ford, on the Rapidan, previously seized by an advance party of three or four smart marching regiments, a small body of one hundred and twenty-five Confederate infantry, guarding the supplies for the rebuilding of the bridge, then in progress, was captured. The cavalry and artillery crossed at once by the ford, as well as a portion of the infantry, the latter wading almost to the armpits. But the construction of the bridge was soon temporarily completed by Gens. Geary and Kane; and the rest of the troops and the pack-mules passed safely, by the light of huge bonfires lighted on the banks. The men were in the highest possible spirits, and testified to their enjoyment of the march by the utmost hilarity. At daylight the Twelfth Corps led the column, Geary in advance. Near the Wilderness, the head of column was attacked from the south by some cavalry and a couple of guns. Stuart had come up from Raccoon Ford the day previous. But a slight demonstration cleared the road; and Stuart retired, sending part of his force to Fredericksburg, and accompanying the rest to Spotsylvania Court House. About two P.M., Thursday, these two corps, under command of Slocum, reached Chancellorsville, and found a portion of the Fifth Corps already in position there. The Twelfth Corps was deployed south of the plank road, with left at the Chancellor House, and the right near Wilderness Church, which line the Eleventh Corps prolonged to the vicinity of Hunting Creek.