the astonishing basaltic columns which form those stupendous masses 

 called the Giant's Causeway, in the north of Ireland, and which also 

 exist in several other parts of the world. The figure of this fossil, 

 given by Lhwyd, yields a correct idea of the manner in which it is 

 amassed together. Volkmann also gives a very accurate representation 

 of the web-like surface which a transverse section of these columns 

 exhibits: and led by this particular appearance, he names this fossil 

 corallium arackriiori, astroites arachnoides, s. telis quasi araneis obtextus, 

 pentagonus, astroites vorticalis* . Indeed, an examination of the ap- 

 p'earance which the stars of this coral yield, especially when mag- 

 nified, will sufficiently countenance the celebrated Volkmann in hesi- 

 tating by which term to designate it, since it readily excites both the 

 idea of the web of a spider, and of the figures which have been 

 sketched to illustrate the vortices of Descartes. 



The lime-stone or marble of which this fossil consists, is generally of 

 an ashen-grey colour, of a compact texture, capable of a good polish, 

 and breaks with a moderate force, laterally applied, into angular 

 ledges. Plate V. Fig. 6. A close examination, especially of its po- 

 lished surface, (see Plate V. Fig. 3.) will shew that the stone is com- 

 posed of a congeries of polygonal columns, exactly adapted, and 

 closely concreted together in a parallel direction : every crack or acci- 

 dental interstice having been filled up by a calcareous spathose matter 

 with which the mass has been pervaded. By this examination it will 

 be seen, that these angular columns vary much in their forms; some 

 having only four, whilst others have five, six, or even seven sides : the 

 pentagon being however the most predominant figure. With respect 

 to their size, the difference is seldom considerable, they being generally 

 abtfut half an inch in diameter: some difference, however, arises from 

 the irregularity of their forms, since one column, filling up the space 

 between three or four others, will be found to be of perhaps double 



* Silesise Subterraneae. Cap. IV. 47. P. 120. Tab. XVIII. Fig. 5, 



