458 



DOMAIN XII. VOLCANIC. 



servation, which I think to be of some import- 

 ance, relative to the glasses I here omit. Several 

 of them have, even in their internal parts, fis- 

 sures frequently an inch in breadth, and three 

 inches in length. These are not entirely vacui- 



Fiiaments. ties, but are frequently crossed by small threads 

 of glass, connected at their two extremities with 

 the sides. The broadest of these threads are 

 four lines in breadth, and the narrowest scarcely 

 a line. When broken they have the fragility of 

 glass, and are found to be a most perfect glass, 

 being colourless, and extremely transparent. It 

 is easy to conceive that these threads have been 

 formed in the same manner with those of the 

 capillary glass, found in similar fissures in the 

 third species of glass. 



" 8. The eighth and last kind of the vitrifi- 

 cations of the Monte della Castagna may be 

 denominated an enamel, that has the colour and 



Unctuous, lustre of asphaltum, of a scaly grain, a very 

 small degree of transparency in the points of 

 the fractures, and of considerable weight and 

 compactness, though it is extremely friable. It 

 is found in solitary masses, not very numerous, 

 and the broken pieces have the property of 

 assuming a globose form. Some of these globes 

 resemble those found by M. Dolomieu in the 

 island of Ponza. I have been favoured with two 



