580 Mr. Hatchett's Analysis of 
This effect on the silver was to be expected ; and I recollect 
to have read, not many months ago, in one of the foreign jour- 
nals, that Mr. Proust had examined an incrustation, of a dark 
grey colour, formed in the course of a very long time, on some 
silver images, in a church at (I believe) Seville. This incrus- 
tation he found to be a compound of silver with sulphur, or, 
in other words, vitreous silver ore. 
The same principle is the cause of the tarnish which silver 
plate contracts with so much ease, particularly in great cities ; 
for this tarnish is principally a commencement of minerali- 
zation on the surface, produced by the sulphureous and he- 
patic vapours dispersed throughout the atmosphere, in such 
places. 
To Mr. Wiseman's observations we are much indebted, as 
they make known the recent and daily formation of martial 
pyrites, and other ores, under certain circumstances. It is not 
to be supposed that such effects are local, or peculiar to Diss 
Mere ; on the contrary, there is reason to believe that similar 
effects, on a larger scale, have been, and are now, daily pro- 
duced in many places. 
The pyrites in coal mines have, probably, in great measure 
thus originated. 
The pyritical wood also may thus have been produced ; and, 
by the subsequent loss of sulphur, and oxidation of the iron, 
this pyritical wood appears to have formed the wood-like iron 
ore which is found in many parts, and particularly in the mines 
on the river Jenisei, in Siberia. 
In short, when the extensive influence of pyrites in the mi- 
neral kingdom, caused by the numerous modifications of it, in 
