The Ouachita structures west of the Mississippi Embayment form a belt extending from the Mexican border to Arkansas. The Rough Creek fault of Kentucky and Illinois is part of a system of faults and steep folds which is similar to the Ouachita structures in its general trend and in the occurrence of thrusting from the south. The Ouachita structures show no sign of diminishing where they pass beneath the Mississippi Embayment on its west side, although the structures of the Rough Creek fault system increase toward the west in the amount of thrusting and in the intensity of deformation. The Rough Creek fault system is considerably north of a projection of the Ouachita deformation across the Mississippi Embayment, but this may be explained by assuming that the belt of deforma ion bends around the Ozark uplift as it bends around the Llano uplift of Texas. Additional evidence is obtained from northwestern Tennessee, where wells in the Mississippi Embayment between the Ouachita and Rough Creek structures have found deformed and altered Paleozoic rocks.