Abstract: A mineral mining installation has a longwall scraper-chain conveyor with a machine, such as a plough, guided for movement back and forth alongside the conveyor to win mineral from a longwall face. A roof support system which may be arranged at the ends of the longwall working, i.e., at the so-called stable zones, is composed of several units each with hydraulic props protected within cylindrical telescopic casings. Each support unit may be displaceable as a whole to follow the working progress or else each support unit may be constructed with front and rear frame assemblies which are relatively displaceable. Each support unit has at least five narrow elongate roof bars disposed closely side-by-side in parallelism. The roof bars are guided for longitudinal advancement and hydraulic rams serve to advance the roof bars individually or in groups. A similar arrangement may also be employed as the floor structure of each support unit.