160 
TAB. CCLXXX. 
urs specimen is remarkable, not only from its being 
unique, but from being found by Mr. Sheffield in Dale- 
head lead-mine, in Cumberland. The vitreous appearance 
might give occasion for dispute between the Neptunians 
and Voicanians; but as I consider both modes of forma- 
tion to be more or Jess concerned in many instances where 
it has been imputed to one only, I shall leave it to every 
philosopher to consider it in his own way, as such a speci- 
men may give equal force to either theory when considered 
alone. 
This specimen consists of a green Oxide or rather Hy- 
drate of Copper united to almost half its weight of Silex. 
It is quite vitreous or glassy in its fracture, with a semi- 
transparency, full of irregular cracks or flaws, like the 
potter’s glaze, or like moderately diluted gum that is 
cracked after being left to dry, and when thinnest, not un- 
like cracked varnish. Its colour and brilliancy are quite 
similar to verdigrise, which is only a preparation from Cop- 
per; nor do we know many other substances which produce 
this beautiful green, which in some mtances approaches the 
green Patina found on old coins. Under the blowpipe its 
brilliancy is lost, and it assumes a dark brown colour, 
but the fragment is difficult of fusion. Small pieces 
thrown into dilute Nitric Acid gradually lose the Copper 
they contain without effervescence, and the Silex remains 
unaltered in form. Of two grains and a half, about one 
erain and a fourth remained transparent when wet, but 
proved opaque white when dry, and possessed the characters 
of Silex. 
