Explanation of Plate I.

Magnified Sections of Vesuvian Minerals

Fig. 1. Section of leucite crystal from the lava of 1868, with fluid cavities. Mag., 350 diams.

" 2, 3, 4, and 5. Sections of nepheline crystals from the lava of 1767, 1834, and 1854.

" 6. Section of sodalite crystal from the lava of 1794, with belonites and crystals of magnetite enclosed.

" 7, 8, 9. Crystals of leucite with microliths and cavities darkened by magnetite dust; also, containing crystals of magnetite.

" 10. Group of leucite crystals of irregular form from the lava of 1855, congregated around a nucleus of crystals of plagioclase and magnetite.