APPENDIX—HALL'S EXPERIMENTS. 143 



on mineral masses, the evident volcanic origin of which 

 was admitted by all. From his original paper we shall ex- 

 tract the results to which this examination led. 



Lava of Catania (Basaltic Lava). 



" After strong heat, the whole was reduced by rapid 

 cooling, to pure black glass ; but, when the heat applied 

 was moderate, the felspars remained unchanged. Being 

 maintained, after a second fusion, in a temperature of 28° 

 (Wedgwood) both these glasses yielded strong and crys- 

 tallized substances somewhat less fusible than the original, 

 and, when exposed to a temperature of 22°, they crystallized 

 rapidly like most of the whins (trap-rocks) into the liver 

 Crystallite. This last property is common to all the lavas." 

 —P. 60. 



Lava of Sta. Venere. 



" The pure black glass formed from this lava yielded, in 

 the regulated heat, the most highly crystallized mass we 

 have obtained from any lava or whin."" — P. 61. 



Lava of La Motta di Catania. 



" Its glass yielded a dark grey crystallite of uniform tex- 

 ture:'— P. 62. 



Lava of Torre del Grecco. 

 "It was found to be less fusible than any of the others, 

 yet its glass crystallized in a lower temperature.' 11 — P. 63. 



Lava of Vesuvius, eruption 1785. 

 Sir James Hall, after examining with care a lava stream 

 which flowed from Vesuvius, found that it completely re- 

 sembled the glass obtained from the rapid cooling of an ar- 



