On some Dolerite-Sills Containing Analcite-Syenite in Central Ayrshire

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Abstract
The petrographical province of analcite-rich rocks in Ayrshire is thoroughly basic in character. The most abundant type is teschenite, which frequently passes into picrite and peridotite. Other thoroughly basic types, such as kylite, essexite, crinanite, and monchiquite, are known ; while the effusive phase of this igneous episode has, in the Mauchline basin, given rise to olivine-basalts, analcite-basanites, nepheline-basalts, monchiquite-lavas, and limburgites, which verge on the ultrabasic. It is all the more interesting, therefore, to find in a few localities subacid rocks rich in analcite, evidently belonging to the same suite. This rock constitutes a new type, analcite-syenite. The rock is so fresh, and the primary character of the analcite so undeniable, that this occurrence must take its place as the principal type of this rock-species. Alkali-syenites and felspathoidal syenites of any description are rare in the British Isles. The best-known examples are found in the remarkable masses of Cnoc-na-Sroine and Loch Ailsh (Suther-land). Prof. S. J. Shand described one of the rocks from the first-named locality as ‘analcite-syenite ’; but in a later paper he withdrew this term, as the analcite was found to be secondary, and he then regarded the rock as merely a leucocratic unspotted variety of borolanite. An analcite-syenite was also described by Hibsch from Grosspriesen in the Bohemian Mittelgebirge, but later the rock was described as sodalite-syenite with a little secondary analcite. Many nepheline-syenites, as, for example, those of Madagascar, contain analcite, some of which Prof. A. Lacroix now believes to be of primary

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