A machine for drying granular materials such as sand and gravel. The machine includes coaxial inner and outer cylinders. Moist sand is introduced into an inlet end of the inner cylinder and gravel is introduced into the inlet end of the outer cylinder. The sand is moved along the inner cylinder by impellers toward the outlet end of the inner cylinder in heat exchange relation with the inner cylinder while the sand is heated to evaporate water therefrom. The heated sand is directed from the outlet end of the inner cylinder into an inlet end portion of the outer cylinder to mix with the gravel. Impeller assemblies mounted on the interior of the outer cylinder raise the sand-gravel mixture as the cyliners rotate to cause the sand-gravel mixture to advance along a space between the cylinders toward the outlet end of the outer cylinder and to cascade against an outer wall of the inner cylinder. Catch plate assemblies mounted on the outer wall of the inner cylinder and extending outwardly therefrom catch the sand-gravel mixture as the sand-gravel mixture cascades against the outer wall of the inner cylinder to hold the sand-gravel mixture in heat exchange relation to the inner cylinder as the cylinders revolve so that an outlet end portion of the inner cylinder can heat the sand-gravel mixture to a sufficient temperature that moisture in the gravel is caused to evaporate, and the sand-gravel mixture is cooled by the moist sand in an inlet end portion of the inner cylinder as the sand-gravel mixture advances to the discharge end of the outer cylinder. The cylinders are driven by a chain which runs on a sectional sprocket mounted on the outer cylinder. Sections of the sectional sprocket are separately mounted on the outer cylinder so that the outer cylinder can flex with changes of temperature of portions thereof.