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per for building, as is the cafe with many 

 other tufas ; but it is merely an argillaceous 

 earth, refembling, from its foftnefs, the 

 hardened mud of rivers. Its colour is a 

 dull grey, its ftru6ture fomevvhat granular, 

 and fo yielding that it may be crumbled and 

 pulverized between the fingers. It is light, 

 adheres flightly to the infide of the lip, 

 emits a feeble argillaceous odour, and, w-hen 

 immerfed in wacer, greedily imbibes it in 

 every part. 



In the furnace it firft acquired a reddifh 

 brown colour, and afterwards the black co- 

 lour of iron. It became fo hard that it 

 gave fparks with fteel, without, however, 

 vitrifying, except that its furface affumed a 

 kind of vitreous varnifli. 



The depth of this tufa is different in 

 different parts of the mountain. In fome 

 places it is feveral feet deep, in others but a 

 few, and in others there is fo great a quan- 

 tity of it that, notwithilanding the excava- 

 tions made in it by the rains, I was unable 



C2 . t© 



