FOREIGN CORRESPONDENCE. 



195 



consider that steam (which in volcanos is frequently acid) may be 

 heated to an enormous extent— we shall readily conceive the production 

 of some varieties of lava by the agency of hot water, acid vapour, and 

 gases, and that of the mud in the Javanese and South American 

 volcanos. Let us add, in conclusion, that the eruptions of mud- 

 volcanos are accompanied or preceded, as in lava-producing mountains, 

 by earthquakes, subterranean thunder, smoke, cinders, &;c. 



Sulphate of potash, as a mineral species, is extremely rare ; it is 

 known to the French mineralogists as Aphthalose; in Italy it goes under 

 the name of Aftalosio, and is occasionally found in small white crystals 

 on the lava of Vesuvius, or as a dry powder in the cavities of the lava. 

 Some time ago Signori Corvelli and Monticelli remarked that the 

 Aftalosio of Vesuvius is generally very impure, being frequently mixed 

 •with salts of copper or iron, but principally with common salt (chlorides 

 of sodium). Signer Barresi, who is at present attached to the faculty 

 of natural history in the University of Palermo, has just discovered, in 

 Sicily, the mineral species of which we speak, in beautifully regular 

 crystals, and perfectly pure. The samples he has collected are looked 

 upon by naturalists with deep curiosity, and the learned professor has 

 written upon his discovery a long paper, which we have not yet had the 

 good fortune to receive. 



If sulphate of potash be excessively rare in nature, the same cannot 

 be said of sulphate of soda, which salt, though quite as soluble in water 

 as the former, exists in enormous quantities near Lodosa, in Spain. 

 Lodosa is a dirty little town on the confines of Navarre, and the 

 province of Old Castillo. The salt is also met with in the mountains of 

 San Adrian and ^Icanadre. M. de Lajonkaire has lately made extensive 

 investigations concerning these important deposits. The following is, 

 for the two mountains just named, the general disposition of the strata 

 where the sulphate of soda exists : — 



1, Vegetable earth ; 2, six to twelve feet of alluvial sand and clay, 

 almost white ; 3, a bed, seventy feet thick, of rolled stones, which 

 are sometimes firmly cemented together by an argillaceous limestone ; 

 4, about 165 feet of a green argillaceous marl, with beds of 

 crystallized gypsum ; 5, twelve to fourteen feet of wine-coloured 



* They are far less important now, however, than formerly. The artificial 

 sulphate of soda manufactured in large quantities from common salt for the use 

 of the glass makers, the artificial production of carbonate of soda, &c., have 

 greatly diminished in value the natural deposits. — T. L. P. 



