The differential sedimentation of a binary suspension was examined experimentally under continuous sedimentation conditions, using a free-settling zone depth of 1.50 m. The feed suspension consisted of a mixture of ballotini with 17.4 +/- 0.2% - 75 + 45 mu m (fine species), and 82.6 +/- 0.2% - 310 + 212 mu m (coarse species) in an aqueous 45 wt.% glycerol solution. The coarse species arrived in the underflow with a well-defined front, achieving steady state within about 0.1 h. The fine species arrived at the same time, but took more than 0.6 h to reach steady state, resulting in a disproportionate accumulation of the fine species and, hence, a free-settling zone composition of 61 +/- 1% fines. The concentration of the fine species ahead of the fines front increased in a first order fashion. It was demonstrated, using a one-dimensional model, that the results could be explained by allowing an erosion of the fines front by the coarse particles, and the formation of a mixing zone between the two fronts.