280 
THE GEOLOGIST. 
twelve mouths or nioi-e, 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 lava, but from its red colour it has evidently been as 
often mistaken for oxide of iron. 
To chemists and minei-alogists this discovery is of the highest 
iuterest. 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 Reiclienstein, and its principal pro- 
perties were made known by the then eminent chemist Klaproth. 
Selenium, which bears much analogy to sulpiiur, was discovered, in 
1817, by the celebrated Berzelius. It has hitherto been found only 
as seleuiuret 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 distingiiished 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 ou the surface of the 
beds of lava. It appears to be another combination of selenium, not 
yet thoroiighly 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 iutei'esting 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 effects 
produced upon the different stratified deposits by the upheaval of 
igneous or plutonic rocks. We will now inquire how the igneous or erup- 
tive roclc itself ia modified while acting upon the strata it has uplifted. 
