Although the mineral gyrolite has long been known to occur in the British Isles, namely in the basalt lavas of Skye, Mull, and the Treshnish Islands, &c., off the west coast of Scotland, and has more recently been described from the cliffs between Ardtornish Bay and the fault of Dearg Allt in Argyllshire on the mainland, no instance of its occurrence in the lavas of the north of Ireland has hitherto been recorded.

The examination, however, of a large number of specimens collected both for me and by myself during the past year and a half has shown that the mineral, though occurring in small quantity relative to the other zeolites with which it is associated, is fairly widely distributed throughout the harder lavas in the neighbourhood of Belfast.