A device for supplying a mixture of pieces of material or fragments of different materials and sizes to one or more receiving units wherein the mixture is supplied to the device within a relatively limited area from where it is distributed to the receiving units so that each of them receives a substantially uniform layer of the mixture at the same time as it is spread out over a wide area. The device comprises one or more vibrating troughs each with a supporting surface at the receiving end and a protuberance centrally mounted in the trough from which the material is spread over the supporting surface (15) during the formation of a uniformly thick layer of material which is carried along the supporting surface to the discharge end of each vibrating trough where it is discharged.