In a paper published sometime ago,(1) I ventured to show how it might be possible to express symbolically the composition and structure of an igneous rock. The type of formula then suggested, though may possess some advantage over the so-called rock formula of Osann, is, for two obvious In a paper published sometime ago, (1) I ventured to show how it might be possible to express symbolically the composition and structure of an igneous rock. The type of formula then suggested, though may possess some advantage over the so-called rock formula of Osann, is, for two obvious