* its colour changes, and-it paffes into aft
4 earthy hate. It is probable that this de->
1 compofition arifes from feme invifible
4 particles of pyrites, which become effloref-
4 cent,, and caufe the fubftance to fall into
4 a detritus.
4 Here then is a proof that galena has
4 been found in a bed of channel, in which
4 it has been traced in an uninterrupted line
4 of 90 feet, accompanied with a fmall por-
4 tion of calcareous and fluor fpar. This
4 inftance exhibits a dired and unequivocal
4 exception to the obfervations hereto made
‘ refpeding the mines of Derbylhire. The
4 exiftence of lead ore in the trapp is a cer-
4 tain proof that it is not the produd of
4 fire.
‘ I know that thofe mineral ogifi's who
4 are cortverfant in the ftudy of lithology,
4 who have examined the trapp upon the
4 fpot, and are fully acquainted with that
ftone
4 ftone and all its varieties have no occafion
4 for this proof. But the fad appeared of fo
4 much importance that I conceived it pro-
4 per to mention it, to do away every
4 doubt on the fubjedi This confideration
4 therefore, will form, my excufe to thofe
4 who may be difpleafed at the minute and
4 tedious details which I have been obliged
4 to enter into, that I might place the
4 queftion in the cleared poffible point of
4 view.’
I am ferry Motif, faujas de St. Fond
did not examine this fubftance more minutely,
as well as the well-known mountain
of Mam Tor.
He fays, page 325 of his work,4 Several
4 mines have been opened in the very fteep
4 calcareous mountain of Mam Tor/
Its very appearance is the moft oppofite
to calcareous mountains that can be conceived,
and its component parts are mica-
F ceous