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their bases, but grow gradually smaller upwards, to about half that 

 thickness at the top ; two columns below often merge into one at about 

 six feet down from the top, and sometimes three at the base join into 

 one above, but that one is thicker than where it separates into two or 

 three lower down. The columns are about 50 feet in height, and form 

 one of the finest as well as the most singular of the columnar facades of 

 Antrim. 



If the view I take of the formation of columnar ranges of trap be 

 correct, this 50 feet layer lying directly on the chalk must have been 

 the last mass of trap erupted at White Head, and injected from its source 

 into this position. Under other circumstances, I should say that the 

 mass lying on the chalk would have been the first. 



The Giant's Causeway has got a name of wide-spread celebrity. It 

 is a low and rather irregular platform of basaltic rock running out north- 

 ward into the sea from the bottom of a high cliff. It resembles a quay 

 or a road, a few feet higher on the east side than on the west. At low 

 water it is about 210 yards long from the passage cut through it at 

 the south to the north end, where its dips into the sea. It is about 50 

 yards wide at the south end, and from 5 to 10 at the point. It is 

 composed of a single layer of basalt about 40 feet thick, reposing nearly 

 in a horizontal position ; this layer is composed of a number of upright 

 columns standing on end, and so closely packed together that the blade 

 of a knife could be scarcely put between any two of them. It forms a 

 polygonal pavement on the top, reminding one of the cells of a honey- 

 comb, or of the wood pavements now pretty well known in large towns ; 

 it is even enough on the surface to walk upon. The columns are from 

 14 to 18 inches in diameter ; every one is a prism, mostly of six sides 

 as it stands on end, but the sides are not equal. Some of the columns 

 have five sides, and a few four ; some also have seven sides or eight, and 

 the guides show one with nine, but there are ten times as many with 

 six sides as there are of all the other put together. 



No two sides of a column are equal ; the six sides of any one column 

 are respectively equal to the adjacent sides of the surrounding columns. 

 "Whether those sides be long or short, they all meet exactly at the 

 angles, where there are no interstices or opens of any kind. A 

 single column is usually bounded by six planes, each a regular pa- 

 rallelogram, from bottom to top, the whole like one long stone, with 

 six angles. Besides the vertical joints which separate the columns, 

 there are cross joints also in every column. Those cross joints are 

 seldom visible when the column is in situ; but when it is quarried, the 

 stone breaks across at every joint. These joints are not regular planes. 

 There is a convex and a concave surface in each, which fit with great 

 exactness. The convex surface is usually uppermost on every piece, 

 but not always. On account of the convex and concave surfaces in a 

 joint, there is always a space where the stone on the concave side is 

 prolonged, and reaches two or three inches over the convex joint at the 

 angle, making there a sharp point. These points are called spurs. They 

 mostly break off in the quarrying. 



E. I. A. PEOC. VOL. X. 2 T 



