FOREIGN CORRESPONDENCE. 
195 
consider that steam (whicli 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, 
hy earthquakes, subterranean thunder, smoke, cinders, Sec. 
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). Signor 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 along 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 dirt}' little town on the confines of Navarre, and the 
province of Old Castille. The salt is also met with in the mountains of 
San Adrian and A.lcanadre. M. de Lajoukaire 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 
sulijhate of soda manufactured in large quantities from common salt for the use 
of the K^'iss makers, the artificial production of carbonate of soda, &c., have 
greatly diminished in value the natural deporjits.---T. L. P. 
