giant's causeway. 



141 



mation. Basaltic columns are frequently seen in countries that are 

 the seat of volcanic fires, but they occur also in countries very re- 

 mote from any known volcanoes. The theories respecting their for- 

 mation will be subsequently adverted to. 



Few countries in the world present more magnificent basaltic co- 

 lumnar ranges than the north part of Ireland, and some of the He- 

 brides : probably these are connected under the ocean, and have had 

 the same origin. 



The Giant's Causeway constitutes a small part of a vast basaltic 

 range, along the north coast of Ireland, in the county of Antrim. 

 The promontory of Fairhead and Borgue, in the same range, are 

 situated eight miles from each other : these capes consist of various 

 ranges of pillars and horizontal strata, which rise from the sea to the 

 height of five hundred feet : from their abruptness they are very con- 

 spicuous, and form a pile of natural architecture, in which the regu- 

 larity and symmetry of art are united with the wild grandeur and 

 magnificence of nature. Many of the columns in the ranges at 

 Fairhead are one hundred and fifty feet in height, and five feet in 

 breadth. At the base along the shore is a wild waste of rocky frag- 

 ments, which have fallen from the cliffs. Immense masses that have 

 withstood the force of the shock lie in groups, resembling the ruins 

 of enormous castles. At the Giant's Causeway, the columns rarely 

 exceed one foot in breadth, and thirty feet in height: they are sharp- 

 ly defined, and the columns are divided into smaller blocks, or prisms 

 of one foot or more in length, which fit neatly into each other, like 

 a ball and socket. The basalt is close grained, but the upper joint 

 is cellular. The columns are most frequently formed with five or 

 six sides ; but some have seven or eight, and others not more than 

 three. Beds of basalt that are not columnar, in some situations lie 

 over and also under the columns. The basalt in these beds is cellu- 

 lar, and contains zeolites in its cavities. The columns at Fairhead 

 are not articulated like those at the Giant's Causeway; but the blocks 

 which are of great length in each column, lie flat on each other. 

 Basalt appears to extend on the coast and inland about forty miles in 

 length and twenty in breadth. 



A full and perspicuous account of the geology of this part of Ire- 

 land is given by Messrs. Buckland and Conybeare, in the fourth vol- 

 ume of the Geological Transactions. It appears that this basaltic 

 range rests upon lias limestone containing marine shells and ammon- 

 ites ; the basalt also enters chalk-rocks, which are much broken by 

 it and in one part a considerable mass of chalk is completely envel- 

 oped in basalt. The effect of a basaltic dyke, in crystallizing the 

 chalk on each side of it, has already been mentioned. Former ob- 

 servers, unacquainted with the nature of the rock on which the ba- 

 saltic ranges of the Giant's Causeway rest, have mistaken it for ba- 

 salt ; it is a dark coloured highly indurated limestone, and as it con- 

 tains shells and other organic remains, these remains were erroneous- 

 ly supposed to prove the marine origin of basalt. 



