AIIRAN. MINERALS. 425 



structure ; as I have more fully pointed out in describing 

 the pitchstone vein of Brodick wood. 



I SHALL now proceed to enumerate the few inde- 

 pendent minerals which have been observed in Arran, 

 the history of its rocks having terminated with that of 

 the pitchstone. 



It was already remarked that smoky quartz was found 

 in cavities in the granite. The crystals sometimes attain 

 a considerable size, and have been collected for orna- 

 mental purposes. The felspar found in the same situ- 

 ations, occasionally also attains sufficient size and regu- 

 larity to find a place in the cabinets of collectors ; in the 

 porphyry of Drumodune, it also occurs in many distinct 

 forms; the crystals being easily detached from the rock 

 in consequence of the decomposition of the base. It is 

 said that adularia is occasionally to be met with in the 

 granite, but it did not fall under my observation. 



Epidote is found in many parts of the island ; entering 

 into the schist, the granite, and the porphyries; but it 

 is neither conspicuous for its beauty, nor for its quantity 

 in any one spot. Augit, mesotype, and the sulphat of 

 barytes were already mentioned in the places where they 

 occur; and they present no interest to justify a more 

 detailed notice. Stilbite, has been observed in cavities 

 in the granite ; in small quantity, and in minute crystals. 

 It occurs in the same manner in Strontian mine ; but 

 excepting in these two instances, its place in Scotland 

 is invariably among the trap rocks. 



It was already remarked that the prehnite found in the 

 augit rock of this island, was in very small concretions, 

 but that it exhibited transitions into quartz, rnesotype, 

 (or nadelstein) and chalcedony. These transitions are 

 very interesting, although here so obscure as not to pre- 

 sent very satisfactory proofs of their real nature. But 

 their existence is confirmed by the occurrence of analo- 



