VI.—The Chawfordjohn Essexite and Associated Rocks

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Abstract
Although the so-called Crawfordjohn essexite has been mentioned several times in petrographic literature, no detailed description of the occurrence has been given. In 1888 Teall described the main rock of the intrusion as an abnormal variety ofthe N. W.-S.E. Kainozoic dykes and noted the porphyritic augite andthe abundance of felspar, olivine, and apatite. Lacroix, in a generalpaper on the teschenites, mentioned the occurrence of nephelite in the same rock, which he described as an “olivine-teschenite, passing instructure to a tephrite”. Bailey, in the Glasgow memoir, remarked on the close similarity between the Crawfordjohn and Lennoxtown rocks and classed them with the essexites on account of their chemical similarity to the Brandberget rocks, while Tyrrell, on account ofthis similarity and also of the resemblance to the Carclout essexite, included them in the late Palaeozoic alkaline group.

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