With the Union army thus divided, Bragg was waiting his terrible opportunity. Instead of being in full retreat, many miles away, his entire army occupied Pigeon Ridge along the valley on the southern side of Lookout Range, into which Thomas and McCook must descend from the Mountain passes. Down the center of this valley runs a little river, the CHICKAMAUGA. On the southern side of this stream, just opposite the pass from which Thomas’s corps of eighteen thousand devoted men would emerge, was concentrated the entire rebel army, waiting to destroy the isolated parts of the Army of the Cumberland in detail. The region occupied by Bragg was covered with dense forests, and he was further concealed by the low heights of Pigeon Ridge. When Thomas’s corps should have debouched from the pass through Lookout Range, and crossed the Chickamauga to ascend Pigeon Ridge, it was to be overwhelmed. Then McCook and Crittenden, sixty-five miles apart, would be separately destroyed. It fortunately happened that General Negley’s division descended from the gap on the 12th, and crossed the Chickamauga several miles in advance of the main body of Thomas’s corps. Unexpectedly, finding the enemy in great force on the opposite ridge, he swiftly withdrew, checked Thomas from further advance, and enabled the corps to take up an impregnable position in the gap through Lookout Range. Thus foiled, Bragg then resolved to strike Crittenden, but eventually failed in this also. These failures gave the alarm. Bragg’s army was not ready for flight but for fight. It was now a matter of life and death for Rosecrans to concentrate his army before battle. Couriers were dispatched at break-neck speed to McCook, sixty-five miles away, and to Crittenden who had pushed on twenty miles beyond Chattanooga, in imaginary pursuit of Bragg. In some absolutely inexplicable way, Bragg failed for four days to make the attack. In those precious days, from September 13th to 17th, Garfield worked night and day, as chief of staff, to reach the scattered divisions, explore the shortest roads through those lofty mountains, and hasten that combination which alone could save the army from destruction. The suspense was terrible. But Bragg lost his opportunity by delaying too long. Heavy reinforcements for him were arriving, and he thought he was growing stronger. On the 17th and 18th Bragg was found to be moving his army up the valley toward Chattanooga, thus extending his right far beyond Rosecrans’s left, with the evident object of throwing his army upon the roads between the Union army and Chattanooga. To meet this, the Union army was moved in the same direction.