 Fabio Colonna, however, had already shown by burning the material to show that "glossopetrae" were organic matter (limestone) rather than soil minerals, in his treatise "De glossopetris dissertatio" published in 1616.Steno added to Colonna's theory a discussion on the differences in composition between glossopetrae and living sharks' teeth, arguing that the chemical composition of fossils could be altered without changing their form, using the contemporary corpuscular theory of matter.Steno's work on shark teeth led him to the question of how any solid object could come to be found inside another solid object, such as a rock or a layer of rock.