In the year 1884 a paper of mine, entitled “The Geology of Monte Somma and Vesuvius,” was published (Quart. Journ. Geol. Soo. vol. xl. pp. 35 to 119), in which I proposed a new explanation for the peculiarities in form of this volcano. An endeavour was made to show that the truncation of Monte Somma by the series of explosive eruptions, especially of Phase VI., had occurred around an eruptive axis different from that which belonged to the period of vesuvian activity, by which the original Somma cone had been built up. Furthermore, a law was enunciated, which is applicable to a very large number of volcanoes, of which, even in Italy, the following examples may be taken in their order of perfection, viz. Eoccamonfina, Mt. Vultura, Etna, Stromboli, Vulcano, and some of the Roman ones. The following are some of the words used: “There is very good reason to deny the concentricity of the great, crater of the Atrio with the original cone of Monte Somma. If within a cone we scoop out an inverted conical hollow around an axis eccentric, but parallel, to that of the solid, we shall have the included space bounded by an annular ridge, not horizontal, but sloping down in the direction of the axis of excavation, and inclined proportionally more, the further the axis of excavation is removed from that of the solid.