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Art. XXV.—On the Black Lead or Graphite qf Borrodale^ of 
Ayrshire^ and of Glenstratlifarraf. By Professor JamesoNo 
C ommunicated by the Author. 
It Is well known, that the most considerable mine of black 
lead in any country, is that of Borrodale in Cumberland, which 
has supplied the market for a long series of years with the pu- 
rest and most esteemed kinds of this useful mineral. Unfortu- 
nately, however, that mine has of late years decreased very 
much in productiveness, and, we are told, at present affords but 
very inconsiderable returns. This circumstance natuirally leads 
us to inquire, if there are any other mines of this mineral in 
Great Britain, which are likely to supply the place of that of 
Borrodale. The mine near New Cumnock, in Ayrshire, and 
that lately opened in Inverness-shire, have afforded considera- 
ble quantities of graphite ; and these, if extensively and regu- 
larly worked, promise an abundant supply. With the view of 
directing the attention of mineralogists to the geognostical distri- 
bution of plumbago, and of encouraging the more extensive work- 
ing of the graphite mines of Scotland, we shall now give a very 
short description of the mines of Borrodale, of Ayrshire, and of 
Glen str athfarrar, 
I.— BoRiionALE Black-Lead Mine, 
The principal rock of this district is clay-slate, which contains 
beds of felspar-porphyry, hornstone-porphyry, and of various 
trap-rocks. The graphite is contained in one of the beds of 
trap, which is partly greenstone, partly amygdaloid. The amyg- 
daloid is slaty, and frequently contains agates ; in this respect 
agreeing with similar rocks found in trap districts. The gra- 
phite occurs inclosed in the trap, in the form of imbedded 
masses and beds, which are occasionally of considerable magni- 
tude. The beds are very variable in thickness, and are fre- ^ 
quently cut off and interrupted by rents or fissures, called by 
the miners Dykes. The principal bed or mass of graphite, is at 
present lost ; and this disappearance is owing, not to the small 
veins of calcareous spar that traverse tlie trap, but entirely to 
the fissures or dykes. 
