A retort is described for the distillation of carbonaceous material, such as coal, oil shale, and the like, for the recovery of hydrocarbon oils, in which the coal is fed on to annular trays which are surrounded by shrouds having projecting rims. The coal is agitated in each of the trays by stirring members which are attached by links and to a rotary structure which is rotated by worm gearing. A gap is provided in each rim through which the material is transferred from each tray to the next succeeding lower tray, and in falling through the gap it drops on to the rim of the shroud of the next succeeding lower tray and the residue finally drops into a trough and a scraper on the rotatable ring directs it into an outlet. Vapors are drawn off through outlets. A central heating space contains a fireclay tube having a combustion chamber with burners at the lower part. The products of combustion pass through openings into the space, and thence through an outlet into a hopper for preheating the coal which is to be supplied to the trays.