4S8 A Chemical Andyfis of Three Species ofWkinJlone, and Ttoe of L&va, 



II. 



A Chemical Analyfis of Three Species oj Whirijione, and Two of Lava, By RoHERT 

 XEifSEor, M. D. F. R. S. i^ F. A. S. Edin. 



,( Concluded from page 415.^ 



ANALYSIS III. 



Whin of the Calton Hill, near Edinburgh. 



HE rock of this hill varies much in different parts ; but its general character is that of 

 porphyry. The piece I chofe for analyfis was taken from the fouth fide, about ten or 

 twelve feet below its higheft point ; and was free from calcareous fpar. 



The external characters of this particular piece are as follow : it confifts of a greyifh 

 bafis, containing rhomboidal cryftals of felfpar of a light reddifti-brown colour ; and fmall 

 fpherical maffes of green earth. The bafis, in its fradure, is uneven, and earthy, and 

 lias no luftrc. It can be fcratched eafily with a knife, and gives an earthy fmell when 

 breathed on. The green earth is foft, and is affedted in fome degree by water ; and being 

 decompofed by the weather, as well as the veins and nodules of calcareous fpar, which are 

 very common in this hill, the rock in many places is extremely porous. 



The fpecimen I have delcribed may be called argillaceous porphyry. It cffervefces 

 flightly with acids ; fo that the lime which it contains muft be united to carbonic acid- Its 

 powder is light grey, with a certain (hade of purple. When heated to rednefs, it becomes 

 of a brown colour. It is not attraded by the magnet, either in its natural ftatc, or after 

 ignition. By being expofed to a low red heat for half an hour, it lofes 5 per cent, of its 

 weight. It foftens at 44 of Wedgwood. Its fpecific gravity is 2.663, as nearly as I could 

 afcertain, from the effeft which the water had in making it crumble down. 

 One hundred parts contain, 



Silex, - - - - - - 50 



Argil, - - - - - - 18.50 



Oxyde of iron, - _ _ _ _ 16.75 



Carbonate of Lime, - - - - " 3 



Moifture, and other vol. matter, _ - - 5 



Soda, about - - - - - 4 



Muriatic acid, about ■ - - - i 



98.25 

 ANALYSIS 



