135 
TAB. CCLXVIII. 
Plumbago in the Rock. 
Tus substance is found in the form of pebbles in rocks, 
making Pudding-Stones, Amygdaloids, anda sort of Traps, 
and seems to have been but little understood by mineralo- 
gical writers. 
The rock is seldem schistose or slaty. It is sometimes 
veined with red Carbonate of Lime; sometimes it consists 
of a grayish or greenish compact steatitic or magnesian mix- 
ture, including the Plumbago, very intimately mixed, or 
in powdery-looking particles, minute pebbles, and other 
forms, some resembling fragments, in common with par- 
ticles of yellow Pyrites, pebbles of Quartz, &c., tightly or 
loosely included *. 
The upper figure represents an amorphous spotted mass 
with the Plumbago, Pyrites, and Quartz pebbles. 
The lower figure has much the resemblance of common 
dark Limestone, and is much impregnated with Plumbago, 
a small mass of which lies on the surface. 
I have a specimen of somewhat largely foliated Plumbago 
holding small cubic ‘yellow Pyrites, varying from a bright 
colour to different states of decomposition, but not passing 
towards Plumbago. I have some Plumbago in a stratified 
piece of Quartz, coloured by red Oxide of Iron: euuerd 
the rock it is found in varies much. 
* Some substance, probably Quartz, runs occasionally among it, re- 
sembling Actynolite, being in longish strix. My friend Mr. Sheffield, in his 
curious collection, has a piece of this, and I was favoured with a specimen 
by the kindness of Mr. Squire. 
