Ashby's ambush and Wheeler's assault shattered McCook's raiders at Brown's Mill as fighting surged through gullied fields and dense thickets south of the present-day Millard Farmer Road. The raiders rallied around a section of the 18th Indiana Battery, whose 2 guns fired shells and canister from beside a log cabin on a commanding ridge, but McCook suffered heavy casualties while Wheeler was reinforced by Brigadier General Robert H. Anderson with 400 Confederate cavalrymen from Flat Shoals and by Philip Roddey with dismounted cavalrymen and several hundred convalescent soldiers from Newnan's four military hospitals. By 5:00 p.m., Wheeler's horseshoe-shaped line had hemmed the raiders in on three sides, and McCook, believing himself completely surrounded by an overwhelming force, announced his intention to surrender. After Jim Brownlow, the 21-year-old colonel of the 1st Tennessee Cavalry, and other officers insisted on trying to break through, McCook allowed the attempt. The raiders disabled their artillery, abandoned ambulances and dozens of dead and wounded, and rode across Sandy Creek, where McCook ordered the 8th Iowa Cavalry to cover the retreat and Wheeler surrounded and captured it. That night Wheeler sent detachments in pursuit, then returned to Newnan and made his headquarters at Buena Vista on LaGrange Street. Meanwhile, three columns of desperate, demoralized Union survivors raced for the river: about 9:00 p.m. remnants of Torrey's brigade reached the Chattahoochee at Williamson's Ferry 15 miles above Franklin and crossed in 3 old canoes while swimming their horses, and about 11:00 p.m. McCook and about 1,200 men reached Philpott's Ferry 9 miles below Franklin, where they refloated the sunken ferryboat and began shuttling men and horses across until the 5th Georgia Cavalry attacked at dawn and captured those stranded on the east bank. McCook then led the survivors on a roundabout retreat through eastern Alabama and western Georgia, reaching Marietta on August 3 after an 8 day odyssey that cost Sherman's cavalry more casualties than any other battle of the Atlanta campaign.