ARMY OF THE POTOMAC follows Lee, 39; order of march, 40; halts at Frederick, Md., 40; change of commanders, 40; dangerous meddling, 41; effect on the army, 42; its _morale_, 43, 44; its efficiency, _note_, 45; in march toward the enemy, 49; diverging while the enemy is concentrating, 52; hard marching, 53; is badly scattered, 53; left wing in a critical position, 54; how posted on June 30, 55; Buford's cavalry engaged at Gettysburg, 62; First Corps gets up to its support, 63; holds the ground till the Eleventh arrives, 68; both are defeated, 76; losses, 77; reasons for defeat, 77; ordered to Gettysburg, 85; Twelfth Corps gets up, 87; also part of Third, 89; other corps, 90; strength of the corps, _note_, 96; as posted July 2 on Cemetery Ridge, 98; Third Corps movements, 101, _et seq._; how this corps was formed to resist Lee's attack, 109; whole of the army up at last, 109; the battle begins, 112; Sickles' whole line is driven in, 124; we hold Little Round Top, 121; portions of the Second and Fifth assist the Third; they have to fall back, 123; other troops compel Longstreet to desist, 125; dispositions for renewing the battle, 133, 134; Culp's Hill attacked, 135; Ewell driven out, 136; sustains a terrific cannonade, 137, 138, 139; lines as formed to resist charge of July 3, 140; the assault repulsed, 143, _et seq._; remains inactive, 153; while Lee retreats, 154; marches in pursuit, 154; finds enemy in a strong position, 156; _notes_, 159; and Lee again slips away, 157; losses during the campaign, 157. Baltimore alarmed, _note_, 45. Baltimore Pike, cutting the Union lines, 99. Battlefield Memorial Association, _note_, 21. Buford's (John) cavalry operations on the left, 40; riding to Fairfield, 49; finds the enemy, 54; is ordered to hold Gettysburg, 55; posts himself on Oak Ridge, 61; fights till relieved, 63; is sent off to the rear, 101. Cavalry, battles of July 3d, 148; operations during Lee's retreat, _notes_, 158. Carlisle, Pa., occupied, 29; evacuated, 51. Cemetery Ridge, described, 15, 16; becomes a rallying-point, July 1, 77; situation afternoon of July 1, 82; Hancock renders it secure, 87; described more in detail, 98, _et seq._; the enemy succeed in scaling it, July 2, 125, 128; but are repulsed, 129; its advantages for defence better availed of, 130. Chambersburg, Pa., occupied by Lee's cavalry, 25; becomes his headquarters, 27.