A belt conveyor for transferring a granular material has an elongated cylindrical housing having opposite ends connecting an inlet end portion to an outlet end portion with each end portion supporting a roller for receiving a flexible endless belt. The belt has a width greater than the diameter of the housing causing the belt to curve upwardly within the housing for form a trough for receiving and transferring the material. To maintain alignment of the belt on the rollers and within the housing, an inner surface of the belt has a continuous flexible guide rib, and each roller has a circumferential groove for receiving the guide rib. To extend the life of the belt and the guide rib, the belt is tensioned by adjusting one of the rollers to space the guide rib above the inner surface of the housing when material is being transferred within the housing.