An apparatus (10) for separating solid materials is described, which comprises a channel (14) for receiving a liquid and the materials to be separated, the channel being provided with an agitation surface. Means for directing streams of fluid (26) at the materials to be separated are provided, the streams of fluid urging the materials over and against the agitation surface to separate the materials. Heavier material is urged along the bottom of the channel to an exit under the action of the streams of fluid, and lighter material separated from the heavier material rises to the surface of the liquid. The agitation surface comprises a plurality of formations (34) each extending across at least a portion of the width of the channel (14), each formation comprising an ascending surface and a descending surface, at least part of the ascending surface having a steeper slope with respect to the base of the channel than the descending surface. It has been found that the shallower descending surface of one formation followed by the steeper ascending surface of the next formation provides an improvement in agitation of the solid materials as they progress down the descending surface and start to progress up the ascending surface, keeps the transition from the descending surface to the ascending surface clear of a build-up of materials, and provides for the lighter materials to be urged upwards at a suitable angle to reach the surface for removal.