Experiments on Whinjlone and Lava, 57 



No. I. Lava of Cata/iia. 



This is the celebrated lava, which, in 1669, laid wade great part of the town of Catania. 

 The interior part of the current (accurately defcribed bjr M. Dolomieu, I/les Ponces, 

 p. 256 *), from which the fubjecl of our experiment was taken, confifts of a light grey 

 bafis, interfperfed with qryftals of felfpar and of fchorl, (augit). It bears a general re- 

 femblance to the rock of the bafaltic columns on Arthur's Seat, and exhibited the fame 

 phenomena in our experiments. After flrong heat, the whole was reduced, by rapid cool- 

 ing, to pure black glafs ; but when the heat applied was moderate, the felfpars remained 

 unchanged. Being maintained, after a fecond fufion, in a temperature of 28, both thefe 

 glaffes yielded ftony and cryftallized fubftances, fomewhat lefs fufible than the original ; 

 and when expofed to a temperature of 22, they cryftallized rapidly, like moft of the whins, 

 into the liver cryftallite. This laft property is common to all the lavas. 



No. 2. Lava of S" Venere. 



This current has flowed in the neighbourhood of a little chapel, called S'* Venere, 

 above the village of Piedimonte, on the north fide of Mount jEtna. Owing to the ftrong 

 vefemblance which it bears to ftones fuppofed not volcanic, we took care that our fpecimens 

 fhould be broken from the aftual current ; and to one of them, though moflly compatt, is 

 attached a fcorified mafs, which had made part of the external furface. The folid part is 

 of a black, or rather dark blue, colour ; very fine grained and homogeneous, having a 

 multitude of minute and {hining facettes vifible in the fun ; in this, and in other circum- 

 ftances, it greatly refembles the rock of Edinburgh caftle. This lava is the fecond in M. 

 Dolomieu's Catalogue, and is well defcribed, p. i86t' 



The pure black glafs formed from this lava yielded, in the regulated heat, the moft 

 highly cryftallized mafs we obtained from any lava or whin. 



No. 3. Lava of La Motta di Catania. 



This is liicewife compaft and homogeneous, but for a number of fmall yellow grains 

 of chryfolite fcattered through it, (defcribed by M. Dolomieu, p. ipij). It has been 

 thrown up by a partial eruption burfting through the fandftone hills which furround Mount 

 ^tna. The fituation' of this mafs is fingular : it refts upon a little hill, formed of loofe 



• " Elle eft formee d'une pate de roche de come giife, a grains fins, melee d'ecailles, et de crlftaux de 

 " feld-fpathdememe couleur; elle contient un tres grand nombre de criftaux de fchorl noir, et de grains de 

 " cryfolites jaunes, les uns et les autres quelquefuis chatoyans, de diiFerentes couleurs dans leurs fraftures. 



" s Cette lave a une caffure feche, et un grain rude, furtout dans le centre des courans; c'eft \\ 



" o\\ elle a toujours conferve une couleur plus claire, qui doit etre celle de fa bafe; fur les bords et les fur- 

 " faces elle s'eft fort noircie ; elle y a acquis une aflez forte aftion fur I'aiguille ainantee que cell? du centre 

 " n'a prefque point." 



-f " Lave homogene noire : fon grain eft fin et ferre, il eft un peu brillant, 'comrae micace lorfqu'on le 

 " prefente au foleil ; fa caffure nette et feche eft concheidc comrae celle du filex." 



X It belongs to the fifth variety of his compaft lavas. 



Vol. IV.— May 1800. I fcoria, 



