Chert, hornftone, or petrofilex, forming
thin luminated beds, near Bradwell,Buxton,
Middleton, &c. &.C.*
The fame fubftance is alfo found exhibiting
entrochi, coralloids, &c. in which
cafe it feems the fecondary petrofilex of
Sauffure.
Of the barytic order the mod general
is the fubftance called cawk, from its re-
fembling chalk, (which is not found in the
north.) It occurs in great quantities, being
the common attendant on lead ore. The
colour is often white, but more frequently
a greyifh white, inclining to the cream
* Dr. Smith in his travels, vol. I. p. 176, mentions a flratnm
of flint running horizontally through the limeftone by the rock
houfe, at Cromford near Matlock. Mr. Kirwan in his geological
effays fays, that it is found in ftrata 1 % feet thick in Derbylhire.
For this he quotes the philofophical tranfaftions. In Peak
fpreft are a variety of chert beds of various thicknefles, fome ar e
in contadb with the granulated limeftone, although limeftone
full of fhells is above it and below it; its colour is of the
dove blue, it adheres to the chert, and is fofter than the other
variety,
tinge,
tinge, which fometimes rifes to the ochre
yellow. It is foft but ponderous : fra&ure
earthy, fometimes fcaly. It often contains
fmall veins of lead ore, as thin as threads ;
and fometimes fmall veins of fluor and
blende. ,
Barytes occafionally occurs cryftallized in
tabulated rhombs, on grit ftone; but more
generally indelicate tabulated cryftals,which
by combination, form fpherical balls. One
variety is ftala£ritic, fometimes with tranf-
parent cryftals, and native fulphur.
The arborefcent barytes is compofed of
ligaments of various colours, interveining
each other, appearing fomewhat like branches
with foliage. A piece now before me
is polilhed, and exhibits dark brown and
lilac figures, beautifully interfperfed with
blue in a geographic form, or like a coloured
map, and affording beautiful contrails.
Barytes in tabulated cryftals, opake white,
g 4 , half