Thomas crossed over the Sand Mountain to Trenton, Georgia, after much difficulty. When Bragg learned that the Union army had crossed the river below him he evacuated Chattanooga during the 8th and 9th of September, moving 26 miles southward to LaFayette, Georgia, behind the Pigeon Mountains. This movement was made in order that he could protect his line of communications and his base of supplies, his base being Atlanta. As the last of Bragg’s army was leaving the city on the morning of September 9th, the 92nd Illinois Mounted Infantry made a reconnaissance on Lookout Mountain. They then entered the city. Crittenden’s corps followed the railroad to Ringgold, then westward to Rock Springs in pursuit of the Confederates. At this latter point, Crittenden was directly between Bragg and Chattanooga. PRELIMINARY MOVEMENTS Rosecrans was led to believe that Bragg was in full retreat to Rome and Atlanta. He had gathered this information from pretended deserters from the Confederate army. However, he was determined to head the Confederates off. He immediately dispatched Thomas and McCook down Lookout Valley to point 26 and 42 miles below Chattanooga where they crossed Lookout Mountain. Thomas moved into McLemore’s Cove; McCook to Alpine and Summerville, Georgia. In planning these movements and making such disposition of his troops, Rosecrans was falling into a trap which had been set for him. Bragg’s army was not in retreat. They had no intentions of retreating. Rosecrans was not aware of the fact that Bragg was not in retreat until about September 12th. His army was divided into three sections. It was at least 60 miles from the left to right of his troops. Meanwhile, Bragg at LaFayette, was opposite the Union center and in position to attack and crush the Union army in detail as they emerged from the mountains. He had already been re-enforced by Buckner from east Tennessee and Walker from Mississippi. He was only awaiting Longstreet’s arrival from Virginia before turning back in an effort to retake Chattanooga. The latter named troops were seasoned veterans who were sent down by Gen. Lee. A great many of them had fought in the battle of Gettysburg. Upon their arrival Bragg ordered the Confederates to turn back toward Chattanooga. His plan was to attack Crittenden and in case Thomas and McCook should arrive they could be taken care of, likewise, in order. Failure of his subordinate officers to comply promptly with these orders caused this opportunity to be lost. Rosecrans, upon learning that Bragg had received heavy re-enforcements and was turning back in an effort to retake Chattanooga, hurriedly ordered the concentration of his forces. McCook, contrary to orders, took a roundabout route from Summerville, causing some delay. However, on September 17th, he joined Thomas and they in turn started their movement to join Crittenden. At this time Crittenden was on the west side of Chickamauga Creek at Lee and Gordon’s Mill.