Description of fusain (fossil substance resembling charcoal) from 3 Mesozoic floras and comparison with charcoal produced by fire. The fusain in question is shown to agree with charcoal in appearance, composition, great stability to wet oxidation and in the end oxidation to a translucent brown material showing the finest details of pits. It agrees also in the equally good preservation of soft parenchyma and woody fibers; and in the association of all above-ground organs of 1 species. This fusain differs from the products of wet decay, whether aerobic or anaerobic. The conclusion reached is that dry distillation by heat is its only possible origin and this means fire. The fusain is abundant and occurs through great thicknesses of rock suggesting widespread and recurrent fires; but its great relative abundance may be due to relative over-representation through its stability, the unburnt plants being subject to decay and total destruction. It is pointed out that if such fire occurred throughout geological time, there would be large areas for species intolerant of climax forest.