EXPERIMENTS on JVHINSTONE and LAVA. 55 



cryftallite, approaching to the ftructure of the original whin- 

 done, No. 4. 



No. 6. Whin from the Water of Lett h. 



It is found in great blocks in the bed of the river, and has 

 been brought there no doubt from a mafs of the fame kind in 

 the mountains above. It confifts of black hornblend, and of 

 a whitifh matter refembling felfpar, as in No. 1. and No. 5. 

 Thefe two fubflances are nearly in equal proportion, and are 

 confufedly and imperfectly cryftallized in minute mafles. If 

 the whitifh fubflance were felfpar, this (lone, as well as that 

 laft mentioned, would be the griinftein of Werner ; but this 

 white fubflance is far more fufible than felfpar, and melts at a 

 lower heat than the hornblend, with which it is mixed. It 

 has an earthy fmell when breathed on, and may be fcratched 

 with difficulty by a knife. 



In fufion and cryftallization it refembled the other whins. 

 A fragment fimilar to this in all refpects, which I found 

 in the neighbourhood of Edinburgh, manifefled fo ftrong a 

 difpofition to cryftallize, that, though cooled in the open air 

 after fufion, it was found ftony in the heart, with a vitreous 

 outfide. When cryftallized, however> with every precaution, 

 it yielded no remarkable refult. 



No. 7. Whin of the Bafaltic Columns of Staffa. 



I received this fpecimen from a gentleman who broke it from 

 the original rock. It is bafalt of a bluifh-black colour. It is fine 

 grained and homogeneous ; and its fracture is uneven. It has 

 a fmall degree of luflre, from a number of minute mining points 

 perceptible in a ftrong light. It gives an earthy fmell when 

 breathed on, and may be fcratched with difficulty by a knife. 

 It yielded a perfect and very hard glafs, which, in a regulated heat, 



produced 



