During recent years, much attention has been directed to the importance of the Rhombic Pyroxenes (Enstatites) as rock-forming minerals. In 1879 Prof. Fouqué showed that hypersthene is a common mineral in the Santorin lavas, and in 1883 Mr. Whitman Cross demonstrated that there exists a large and important class of andesites, distinguished by the presence in them of the same mineral hypersthene. Mr. Teall, in the pages of this Magazine, has pointed out that similar lavas exist in this country, which are undoubtedly of pre-Tertiary age; and, now that the attention of geologists has been very generally drawn to the subject, the same rocks have been recognized by many observers in all parts of the globe.