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This lava, which has for its bafe the horn'» 

 ftone, and emits a ftrong argillaceous odour ^ 

 has the colour of a dead leaf, a grain fome- 

 what Tandy, and a great number of round 

 pores, from thofe of a fize fcarcely difcerni- 

 ble, to others feven lines in diameter. Many 

 of thefe pores are occupied by cryftallized 

 globules of carbonate of lime, produced by 

 filtration. This lava has the external appear^ 

 ance of being very ancient. In the furnace 

 it affords one of the ufual black and opake 

 enamels. 



To the fouth-Vv-eft of a decliWty of Rua 

 we find great m.affes of a volcanic rock that 

 has fallen down, the feltfpars of which are 

 an exception to thofe of the innumerable 

 lavas defcribed in this work on account of 

 the extraneous bodies enclofed within them. 

 This rock, the different pieces of which are 

 of different colours (fome being afh-grey, 

 others red, others of a pale violet), is of a 

 petrofiliceous bafe, with an earthy grain, 

 and contains, hefides hexagonal micas with 

 oblique fides, tranfparenc feltfpars, cubical, 



prifmatical^ 



