The following notes have been compiled in order that, pending the publication of the results of microscopic and chemical examination of the specimens collected, geologists visiting the island may have an accurate localization of the dykes and intrusive sheets bearing glassy selvages observed by the writer and Mr. J. Lomas, A.N.S.S., during a recent visit to Mull. The list includes, for the sake of completeness, three occurrences of tachylyte which have already been described, viz.:—Some and Gribun1 and Ardtun.