ONE mile due east of Tantallon Castle, on the East Lothian coast, there stands a conspicuous tower or beacon. Its purpose is to afford an offshore warning to mariners. It has been constructed upon the seaward extremity of a northerly-extending ridge of volcanic ash or agglomerate. In recent years the rocks exposed here have been carefully examined by a well-known Edinburgh geologist, the late Mr. T. Cuthbert Day, and his results are reported in an interesting paper entitled “Volcanic Vents on the Coast, from Tantallon Castle eastwards to Peffer Sands, and at Whitberry Point” (Trans. Edin. Geol. Soc., xii, 1930, p. 213). Mr. Day thought that the ash and agglomerate lying south of the beacon represented the materials belonging to two contiguous but distinct volcanic vents of Lower Carboniferous age. To the twin orifices he applied the designation—“ The Car Double Vent.” In the northerly vent there occur two basaltic intrusions intersecting the pyroclastic rock. One of these, an irregular 4 ft. dyke, trends north-west hard by the easterly side of the beacon. The other, an oval plug covering 500 square feet, or thereby, is situated about 100 yards to the south-east. Both masses were determined petrographically by Mr. Day as “ dark red basalt with conspicuous dark crystals of augite, somewhat decomposed, but appearing under the microscope to approach a limburgitic type ”. It is in reference to these “ limburgitic ” intrusions that I present the following brief note, because, lately, I have discovered that they consist of leucite-basanite, a rock of basic felspathoidal character not previously known to occur in this country.