The mineral leucite is not a rock-maker of the first magnitude, but it has nevertheless attracted special interest because of its abundance where found. This latter characteristic places it in the group of feldspathoids, which in a minor way have the same important relations to the classification of igneous rocks as do the feldspars themselves. It is the general impression that up to 1868 but three leucite localities were known,†
namely, the Italian volcanoes, especially Vesuvius, the Laacher See, and the Kaiserstuhl in the Black Forest. Humboldt described the mineral as essentially a European one. The introduction of the microscope) and especially its employment by Zirkel in the preparation of his work on the basaltic rocks,* brought to light a number of other localities in Saxony, Bohemia, Thuringia, and the Rhön mountains,† all of which were, however, European. In 1874 it was discovered . . .