The mineral Leucite has for so long a period been considered as one of the most remarkable examples of limited distribution both in space and time, that the discovery in Australia of a rock largely composed of this mineral, by Mr. T. W. Edgeworth David, F.G.S., of the Geological Survey of New South Wales, is one that appears deserving of being at once placed upon record.

Leucite-crystals, under the head of "white garnet," or "white schorls," appear to have been known from a very early period ; and, indeed, the fine examples from Somma could scarcely fail to attract the attention of the older mineralogists. Subsequently it was found that the mineral occurs in other parts of Italy, and especially the neighbourhood of Rome, as well as at the Laacher See and the Kaiserstuhl.