121 
decomposition of a primitive rock where it was least ex- 
pected ; and the Oxide of Tin, which, in most cases, seems 
coeval with the common Chlorite, Slate Rock, or Killas of 
the Cornish miners, seems again crystallized, if I may use 
the expression; and these new crystals generally differ 
from the former, and are truly curious as to the variety of 
their modifications, being excellent practice for a crystal- 
lographer. The Chlorite which serves to cement the 
pebbles, as before observed, is crystallized; and I find it, 
like tab. 182 of this work, in six-sided plates. Among 
the partly crystallized Quartz in my specimen, are some 
rather shattered interrupted fragments of white Fluor *. 
The Sulphuret of Copper, or Copper Pyrites, is rather in 
amorphous fragments, and there are some very brilliant 
crystals of Arsenical Iron, or Mispickel, a few of which 
are beautifully iridescent. 
Besides the specimens which I have received from Dr. 
Penneck and Mr. Carne, I have been favoured with one 
by Dr. Turton, showing the Sulpburet of Copper. 
* This has so much the appearance of shattered Quartz at first sight, that 
I imagine it might be all taken for Quartz. It burns beautifully phospho- 
rescent ; which is rather curious for white Fluor. 
