280 



THE GEOLOGIST. 



twelve mouths or more, M. Napoli found that it contained a consider- 

 able proportion of selenium and tellurium, combined with titanium, 

 iron, and lead. 



As the lava cools, the sulphurous acid vapours, which are exhaled 

 in abundance from it, partially destroy these combinations of selenium 

 and tellurium, producing a great quantity of pure selenium, which 

 is deposited, and oxides of selenium and tellurium, which are disen- 

 gaged and emitted into the air in a gaseous state and in large 

 proportions. 



Pure Selenium is thus deposited in the cavities and crevices of the 

 lava, and in the interior of the solidified mass. No one had ever 

 remarked this before. Doubtless Selenium has often been seen in 

 the fissures of la^a, but from its red colour it has evidently been as 

 often mistaken for oxide of iron. 



To chemists and mineralogists this discovery is of the highest 

 interest. Both tellurium and selenium are such rare substances that 

 they are only known as curiosities of the laboratory ; and few labora- 

 tories indeed possess specimens of either. 



Up to the present time, tellurium has been found, but very rarely, 

 combined with gold, silver, lead, and bismuth, in the mines of 

 Transylvania. In appearance it resembles antimony. It was dis- 

 covered, in 1782, by Miiller, of Reichenstein, and its principal pro- 

 perties were made known by the then eminent chemist Klaproth. 



Selenium, which bears much analogy to sulphur, was discovered, in 

 1817, by the celebrated Berzelius. It has hitherto been found only 

 as seleniuret of lead, a rare mineral, or combined in certain varieties 

 of iron-pyrites. A native seleniuret of copper was discovered some 

 years ago, and called Berzeline, in honour of the great chemist whom 

 we have just named. Before the interesting observations of M. Napoli, 

 selenium had never been found in nature otherwise than in combina- 

 tion with substances. M. Napoli has also described a new substance, 

 which appears to be a combination of lead and selenium, discovered 

 by M. Palmieri, the distinguished meteorologist of Vesuvius, in cer- 

 tain fumarolle, and which has been named Sacchite, in honour of 

 Professor Sacchi, of Naples. A peculiar white substance has likewise 

 been observed. This substance exists in the crevices of the lava, 

 whence it is easily volatilised, mixes itself with the air, absorbs 

 moisture, and falls again, forming a sort of crust on the surface of the 

 beds of lava. It appears to be another combination of selenium, not 

 yet thoroughly known. We shall return again to these new minerals 

 when we have seen M. Napoli's memoir ; we may already affirm that 

 a new mine of interesting mineral and chemical products is open at 

 Vesuvius, and promises fairly to be a rich one. 



We now resume M. Delesse's researches on metamorphism. In 

 The Geologist for May last we terminated our sketch of the efifects 

 produced upon the different stratified deposits by the upheaval of 

 igneous or plutonic rocks. We will now inquire how the igneous or erup- 

 tive rock itself is modified while acting upon the strata it has uplifted. 



