The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 2: Two Years of Grim War.
Francis Trevelyan Miller, Ed.

Confederate pickets, taken by surprise, retreated from the first line of earthworks, and Thomas, with little loss to either side, captured Orchard Knob, between Chattanooga and Missionary Ridge. From this point, which was almost a mile in advance of the position occupied during the morning, Grant directed the movements of his army on the following day.

the Federal position was of less extent than that occupied by the Confederates. Sherman was in command of the left wing, while Thomas held the center, and “fighting Joe” Hooker, with the Union right in Lookout Valley, threatened Lookout Mountain. The plan of battle was for Sherman to engage the Confederate right and sever communications between Bragg and Longstreet; Hooker was to carry out an assault on the Southern left flank, and at the same time maintain connection with Bridgeport. With both wings assailed by a superior force, it was believed that Bragg must reenforce these positions and permit Thomas, with overwhelming numbers, to concentrate upon the center.

on the 24th, two distinct movements were in progress. Sherman met with but little opposition in his initial attack upon the Confederate right and promptly seized and occupied the north end of Missionary Ridge. The Confederates, late in the afternoon, fought desperately to regain the hill but were finally repulsed, and Sherman fortified the position he had gained. In the mean time, Hooker, early in the day, had begun his operations against Lookout Mountain. Standing like a lone sentinel above the surrounding valleys, its steep, rocky, and deeply furrowed slopes, rising into a high, palisaded crest, frowned defiance upon the advancing troops, while a well-constructed line of defenses completed the imposing barrier.

Hooker had in addition to his own troops a division of Sherman's army (Osterhaus') which, owing to damage to the pontoon bridge at Brown's Ferry, had been prevented from joining its own leader. As ordered by Hooker, General Geary took his division up the Valley to Wauhatchie, crossed the creek