Irish Volcanoes. 183 



precisely like the first, and not to be distinguished from it. 

 This is repeated so often as to indicate a system. The result 

 is recognized by the guides, who describe such centres as the 

 " Lovers' Chair/' the " Giants' Chair/' etc. The whole area 

 of tops of columns may be grouped in imagination into a 

 number of circles, neither intersecting nor squeezing each 

 other, but simply passing into each other almost insensibly. 



If we take a particular column, selecting of course a good 

 and fair example, it is easy to see that it is broken up by 

 joints into frustra, each of which has one end convex or 

 rounded, and the other concave or hollow. Two adjacent 

 surfaces generally correspond, the rounded part of one fitting 

 the hollow surface of the other. This is easily seen, for 

 numerous little pools of fresh or salt water collect in the 

 depressed or hollowed part of the stones when that part is 

 uppermost. 



While the columns remain in their natural condition, the 

 upper and lower surfaces fit closely ; but when exposed to the 

 weather, a little moisture enters and discolours the rock. This 

 causes decomposition, and towards the cliff, where vegetation 

 can take root, it is curious to observe a matted mass of roots 

 penetrating far within the apparently solid stone to a depth of 

 some yards below the surface. 



The appearance of the Causeway is that of a tesselated pave- 

 ment somewhat irregular as to level, but of which the tesseras 

 or paving stones are extremely irregular. A careless observer 

 might suppose that all were of the same size, and all the sides 

 equal, both in number and length. It is only necessary to ob- 

 serve a little more closely to discover that this apparent uni- 

 formity is really made up of very discordant parts. Most of 

 the stones are either five, six, or seven-sided, and it is 

 easy to see that the six-sided figure is that which rules all 

 the others. The perfect form of the section of the column 

 is, beyond doubt, a hexagon or six-sided figure, all the six sides 

 being of equal length. It is the section exhibited by a slice of 

 honey-comb, placed upright so as not to lose any of the honey. 

 But no two columns of the Causeway are exactly alike, and 

 modifications occur in the actual dimensions of the columns and 

 in the difference of length of the sides. Although, however, 

 this difference might be expected to yield a result altogether 

 indefinite, there are, in fact, very well-marked limits to the 

 irregularity. Four-sided figures are very rare indeed, eight- 

 sided figures almost equally so ; and hardly a column of the 

 40,000 of which the Causeway is believed to consist has more 

 than eight or less than four sides. The angles are generally 

 very sharp. In point of dimensions, also, the columns are 

 marvellously regular, hardly any being more than two feet in 



