1,6 Exper'itnenls on Whinjlone and Lava. 



be the griinftein of Werner ; but this white fubftance is far more fufible than felfpar, and 

 melts at a lower heat than the hornbiend, 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 refpedls, which I found in the neighbourhood of Edinburgh, manifefted fo ftrong a 

 difpofition to cryflallize, that, though cooled in the open air after fuGon, 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 Balfaltic Columns ofStaffa. 



I received this fpecimen from a gentleman who broke it from the original rock. It i« 

 bafalt of a bluifli-black colour. It is fine grained and homogeneous ; and its frafture is 

 uneven. It has a fmall degree of luftre, from a number of minute fliining points percep- 

 tible in a ftrong light. It gives an earthy fmell when breathed on, and may be fcratched 

 with difficulty by a knife. It yielded a perfeiSl and very hard glafs, which, in a regulated 

 heat, produced a uniform ftony cryftallite, greatly refcmbling the original. 



It has thus been fliown, that all the whins employed aflume, after fufion, a ftony cha- 

 ra£ler, in confequence of flow cooling ; and the fuccefs of thefe experiments, with fo many 

 varieties, entitles us to afcribe the fame property to the whole clafs. The arguments, 

 therefore, againft the fubcerraneous fufion of whinftone, derived from its ftony charader, 

 ieem now to be fully refuted. 



Experiments on Lava. 



In the inveftigation of Dr. Mutton's fyftem, great advantage may be expected from an 

 examination of lavas. They have undoubtedly flowed on the furface by means of heat ; 

 and whinftone, according to his hypothefis, having flowed in the bowels of the earth by the 

 influence of the fame agent, the two clafles ought to poflefs many properties in common, 

 by which the hiftory of both may be illuftrated. 



I have been enabled to inftitute a comparifon between them, by means of a cabinet of 

 volcanic produdtions which I coUefted in 1785, in company with Dr. J. Home of this So- 

 ciety, on Vefuvious, JEtna, and the Lipari Ifles. On this occafion we were greatly affifted 

 by the celebrated M. Dolomieu*, who accompanied us in part of our expedition. This 

 author complains, in his writings, that travellers, in collefting volcanic produftions, have 

 brought away only the fuperficial fcoria of lavas, which nearly refemble each other in all 



* Though I differ widely from this gentlsman in many of his theoretical opinions, I cannot too ftrongly 

 exprefs my admiration of his merit as a natural hiftorian. His defcriptions of countries, as well as of 

 minerals, prefent the moft lively reprefentations to the mind of the reader, which, in the numerous inftances 

 1 have witnelTed, are perfeftly corrcil. 



4 " cafes. 



