I have been lately examining in conjunction with Prof. Hull a a large series of lavas from Vesuvius, which were collected by Prof. Ouiscardi, of the University of Naples, with a view of determining whether, in the space of 300 years, any difference had occurred in the composition of the lava flow. In the course of this investigation a much more important question arose, viz. :—What is the proportion of each mineral present in the lava, and why does that proportion exist ?

The rock is composed of unknown quantities of nine minerals, of known composition viz.: Leucite, Plagioclase, Magnetite, Olivine, Augite, Hornblende, Mica, Nephcline, and Sodalite, together with an unknown quantity of a paste of unknown composition; from which it is easy to shew that the unknown quantities exceed the number of equations; and consequently, the discussion of the composition of the rock belongs to a branch of the Indeterminate Analysis.