Exptrimints on Whin/lone and Lava. ig 



but for a few minute air bubbles vifible in the artificial cryftallite. The glafs is lefs fufible 

 than that of No. i. and fecms not to poflefs the property of producing the liver cryf- 

 tallite. 



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



Its bafis is a bafalt of a dark grey colour, and uneven frafture. It contains numerous 

 laminar cryftals of felfpar, which. feem to be almofl: colourlefs, and have confiderable luftre 

 and tranfparency. 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 changed to pure black glafs; but 

 in a more moderate heat, (about 60), the felfpar remained unchanged, while the horn- 

 blend difappeared, and formed a glafs along with the bafis of the (tone. Both kinds of glafs 

 yielded highly charaQewfed cryftallites ; that laft mentioned, having its felfpars entire, 

 produced a fubftance like porphyry, in which the white felfpars were embedded in a black 

 cryftalline bafis. The cryftals formed in this bafis are fo complete in one example, that 

 they are feen projefting into the cavities, and ftanding ereft on the external furface, fo as 

 to make it fparkle all over. Thefe black cryftals feem to be hornblend of new formation.. 

 We have found, by fome late experiments, that they are confiderably more refra£lory than 

 the cryftallite in which they lie, and are equally infufible with fome fpecies of natural horn- 

 blend. 



No. 4. Whin from the J^eighhourhood of Duddingjlone Loch. 



It has for its bafis a black bafalt of an uneven frafture. In it are embedded augit in 

 numerous cryftals, felfpar in a fmaller proportion, and difperfed grains of olivin. The fel- 

 fpar feems to be greenifti-white, with confiderable luftre and tranfparency. The ftone gives 

 fire with fteel, and has a flight earthy fmell when breathed on. Its glafs yields a fine 

 grained tryftallite, like that of No. i. 



No. 5. Whin of Salijhury Craig near Edinburgh. 

 This fpecies is an aggregate of black hornblend, and of a greenilh-white matter, both in 

 minute grains. The greenifh-white matter refembles felfpar, but is much more fufible. 

 The general characters are nearly the fame with'thofe of the fpecimen already defcrlbcd,. 

 No. I. It has confiderable luftre, chiefly from the hornblend; an earthy fmell when 

 breathed on } and gives fome fparks with fteel. Its glafs yielded a highly facetted cryftal- 

 lite, approaching to the ftrufture of the original whinftone, No. 4. 



No. 6. Whin from the Water of Leith. 



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. In confifts of black hornblend, and 

 of a whitifh matter refembling felfpar, as in No. i. and No. 5. Thefe two fubftances arc 

 nearly in equal proportion, and are confufedly and imperfectly cryftallized in minute mafles^ 

 If the whitifli fubftance were felfpar, this ftone,^ as well as that laft mentioned, would 



3 be 



