104 



concealment, are by no means inclined to make 

 known the spots, whence they obtain native 

 alum ; but this must be abundant, for I have 

 seen very considerable quantities in their pos- 

 session at a time. It would be of importance 

 to the government of Venezuela, to establish 

 regular works, either of the ore we have just 

 described, or in the aluminous slate that accom- 

 panies it. The latter might be roasted, lixi- 

 viated, and concentrated (by graduation) by the 

 fervent Sun of the tropics. 



South America at present receives it's alum 

 from Europe, as Europe in it's turn received it 

 from the natives of Asia till the fifteenth cen- 

 tury. Mineralogists, before my travels, knew 

 no other substances, which, without addition, 

 calcined or not calcined, could directly yield 

 alum (sulphat of alumin and potash), except 

 rocks of trachytic formation, and small veins 

 traversing beds of lignite and bituminous wood. 

 Both these substances, of so different an origin, 

 contain all that constitutes alum, that is to say, 

 alumin, sulphuric acid, and potash. The ores 

 of Tolfa, Milo, and Nipoligo ; those of Montione, 

 in which silica does not accompany the alumin ; 

 the siliceous breccia of Mont-Dore, so well de~ 



the alpine limestone of Cumanacoa? Vol. iii, p. 76. Fibrous 

 alum is found in Europe only in formations posterior to those 

 of transition, in lignites, and other tertiary formations that 

 belong to the lignites. 



