V.–On the occurrence of a Blue Amphibole in a Hornblende Kersantite from Co. Down

In connection with the revision of the Silurian area in Ireland, at present in progress by the staff of the Irish branch of the Geological Survey, a number of rock-specimens of the dykes occurring on the coast of Co. Down were lately petrographically examined by the writer, who detected in one of the slices a blue amphibole of secondary origin. As a mineral of this kind was not hitherto known to occur in sitû in Ireland, it may be of interest to put its discovery on record here and to give also a few details respecting its characteristics.