various parts of Scotland. 405 



edges of the plates which have formed them. But the most 

 common of the spherical bodies are, when fresh broken, of a white 

 colour, becoming at first yellow by exposure to air, and subsequently 

 of a dark brown. Their internal texture, as far as it can be deter- 

 mined by high magnifying powers, appears platy, and although it 

 is difficult to speak with certainty of bodies so minute, and so much 

 out of the reach of examination, they seem greatly to resemble 

 brown spar ; a conclusion rendered more probable, by the changes 

 which they undergo on exposure to the air. The whole of these 

 chalcedonies are occasionally penetrated by laminse of calcareous 

 spar, which are often so numerous as to form nearly one half 

 of the stone, and which from its yielding in their direction, 

 rather than in that of the chalcedony, do often seem on a su- 

 perficial view to form the whole of it. In the rifts of these 

 chalcedonies, we may occasionally find detached masses of green 

 earth, which by its combination with the stone itself appears 

 beyond all doubt to be the colouring ingredient. Its unequal 

 diffusion through the stone, is equally demonstrative of the same 

 supposition. 



We have now to compare the green chalcedony of Rum, with 

 the stone known by the name of heliotrope, and commonly called 

 oriental^ since that name has been applied to it, and as it will appear, 

 with perfect propriety. The fracture and translucency of the true 

 oriental heliotrope, show, as Brongnlart has well remarked, that 

 it has been improperly ranked among the jaspers ; and the de- 

 scription and natural analysis, if I may so call it, which I have 

 now given of the stone of Rum, confirm the propriety of his 

 remark, and refer it to its true place among the varieties of 

 chalcedony. It is true, that the stone of Rum very rarely exhibits 

 the red spots which so often occur in the oriental kinds, but these 



