EXPERIMENTS on WHINSTONE and LAVA. 5: 



No. 2. Whin of the Rock of Edinburgh Cajlle. 



This is a bafalt of a blackifh blue colour. Its grain is fine, 

 and its fracture uneven, partaking of the fplintery. It is in ge- 

 neral homogeneous, although, in fome pieces, a very few mi- 

 nute cryftals of hornblend are perceptible. It has fome luftre, 

 from a number of fmall mining facettes ; has an earthy fmell 

 when breathed on ; and gives fire flightly with fteel. 



The pure glafs which this whin yielded, by rapid cooling 

 after a moderate heat, was cryftallized in three experiments, 

 and produced mafTes greatly refembling the original. In one of 

 thefe, formed on a large fcale in the glafs-houfe, the refem- 

 blance is fo ftrong, both as to colour and texture, that it would 

 be difficult, or perhaps impoffible, to diftinguifh them, but for 

 a few minute air bubbles vifible in the artificial cryftallite. 

 The glafs is lefs fufible than that of No. 1. and feems not to 

 pofTefs the property of producing the liver cryftallite. 



No. 3. Whin of the Bafaltic Columns on Arthur's Seat, near 



Edinburgh. 



Its bafis is a bafalt of a dark grey colour, and uneven fracture. 

 It contains numerous laminar cryftals of felfpar, which feem 

 to be almoft colourlefs, and have considerable luftre and tran- 

 fparency. It alfo contains fome black hornblend. It has an 

 earthy fmell when breathed on, and gives fparks flightly with 

 fteel.' 



In the temperature of 100, or upwards, the whole was chan- 

 ged to pure black glafs ; but in a more moderate heat, (about 

 60), the felfpar remained unchanged, while the hornblend dis- 

 appeared, and formed a glafs along with the bafis of the ftone. 



Both 



