GIANT'S CAUSEWAY, a promontory of columnar basalt, on the north coast of Co. Antrim, Ireland. It is divided by whin dykes into the Little Causeway, the Middle Causeway and the Larger or Grand Causeway. The pillars composing it are for the most part irregular hexagons. In diameter they vary from 15 to 20 in., and some are 20 ft. in height. The Great Causeway is in some places nearly 4o ft. in breadth and is highest at its nar rowest part. It extends outwards into a platform and for nearly yd. is above water. The neighbouring cliffs, particularly in the bay to the east, exhibit in many places similar columns. The most remarkable of the cliffs is the Pleaskin, the upper pillars of which are 6o ft. in height ; beneath these is a mass of coarse black amyg daloid, of the same thickness, underlain by a second range of ba saltic pillars, from 4o to 5o ft. in height. Near the Giant's Cause way are the ruins of the castles of Dunseverick and Dunluce, situated on isolated crags. In 1883 an electric railway, the first in the United Kingdom, was opened, connecting the Causeway with Portrush and Bushmills.