The Heart of the Hills is the third volume in Fox, Jr.'s Mountain Trilogy. In it, Fox revises his earlier thoughts about mountain people. He depicts more clearly than in his previous work just how they were exploited by outside industrialists—those men who, in the words of Fox's hero Jason Hawn, "got rich diggin' our coal an' cuttin' our timber." He also reveals the long-term impact of this exploitation on the environment (University of Kentucky).