THE preparations of the engineer-in-chief for the coming reckoning with Bragg were of two kinds. One was the completion of the defensive works at Chattanooga. Heavy details of men were made and the work pushed day and night, and, on the day fixed for the attack on the enemy, the fortifications were pronounced in a sufficiently advanced condition to defy any assault. The other was the collection of enough material for two bridges. One was to be thrown over the Tennessee, which was 1300 feet wide at the selected point, and another across the Chickamauga, at its mouth, of a width of 180 feet. The spare pontoons scattered between Chattanooga and Bridgeport were gathered together by strenuous efforts, and the two sawmills of the town put in operation to furnish the rest of the material wanted. It was decided, in order to screen the movement from the observation of the enemy, to haul the pontoons by land to a point opposite the mouth of the North Chickamauga, some six miles north of Chattanooga, and to float and load them there with the first landing force and row them to the landing-point. On November 20, the boats were in the river, provided with oars and crews. Then a formidable obstacle to the laying of the pontoon-bridges arose. The Tennessee in its actual swollen stage brought down great quantities of heavy drift-wood, which broke both the pontoon-bridges at Chattanooga and Brown's Ferry. This naturally gave rise to the fear that it would not be possible to throw the two bridges for Sherman, or to maintain them, if thrown, long enough for the passage of the troops.