88 Sketch of the Mineralogy 



this species of rock, which there can be no hesitation 

 in pronouncing to be what is called ivhin stone in Scot- 

 land, trap in Sweden, and basalt in some countries. 

 The Giant's Causeway in Ireland, and the Cave of Fin- 

 sarA in the island of Staffa, on the vv^estern coast of Scot- 

 land, ai'e famous, all the world over, for an exhibition of 

 basaltic pillars of astonishing size, number and regu- 

 larity. 



The southern side of the mountain called Arthur's 

 Seat, at Edinburgh, exhibits regular six-sided prisms, 

 and our rocks here show a similar tendency so strongly, 

 that one would, from this circumstance alone, be induced 

 to suspect their identity. 



But the matter is placed beyond all doubt by a mi- 

 nute ocular comparison of specimens from the two coun- 

 tries. The writer is in possession of specimens of the 

 different basaltic rocks which are found in the vicinity of 

 Edinburgh, and, on comparing a piece of our East Rock, 

 with a piece of Salisbury Craig, a basaltic mountain near 

 that city, one would be ready to say that they were bro- 

 ken from the same mass. Salisbury Craig is, in appear- 

 ance, strikingly similar to the East Rock. It has the 

 same rude perpendicular columns, the same curvilinear 

 form, and nearly the same extent : It has a similai' slo- 

 ping mass of ruins accumulated at its foot ; it fronts the 

 same way ; it slopes off with the same easy declivity in 

 the rear : Like the East Rock, it reposes on a bed of 

 red sand stone ; and finally, on fracture, the stone pre- 

 sents the same appearance. So far as it has been exam- 

 ined, its chemical characters appear to be the same. 

 It melts in the heat of a smith's forge, and, on cooling 

 rapidly, presents the same vitreous slag, which the Scotch 

 whin is known to produce. Hornblende and a white 

 substance softer than quartz, probably feldspar, are the 

 principal ingredients of both. The stone is reckoned 

 among the argillaceous class, by some mineralogists, and 

 by others, among the siliceous. The predominant in- 

 gredient is certainly silex, or the flinty earth, although 

 when breathed upon, it emits the smell of clay^ which 

 would induce one to refer it to the argillaceous family. 



