On the occurrence of sillimanite gneisses in Central Anglesey

T he author records the occurrence of gneisses and schists containing Sillimanite among the rocks associated with the granites of Central Anglesey. The Sillimanite occurs partly as fine needles in quartz (“ Faserkiesel ”), partly as matted bundles in brown, mica (“ shimmer-aggregates ”). Sections near the Holyhead Road show that the granite penetrates the schists in a complicated series of sills, which, though lying for the most part between parallel folia, demonstrate their intrusive character by frequent transgressive junction and by containing many included fragments of the schists. No chilled edges have been observed. The whole series of phenomena appears to be of the same nature as those observed by Mr J. Horne and the author in Eastern Sutherland (Q.J.G.S., 1896, p. 633).