43 
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 arachnion, astroites arachnoides, s. telis quasi araneis ohtextus, 
pe 7 itagonus, astroites vo7'ticalis.^ Indeed, an examination of the ap- 
pearance which the stars of this coral yield, especially when magnified, 
will sufficiently countenance the celebrated Volkmann in hesitating 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 
about 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 
* SilesiEe Subterraneae. Cap. IV. §47. P. 120. Tab, XVIII, Fig. 5. 
