402 Dr. T. Thomson on the Minerals 



lead, which occurs in the mine in all the different varieties 

 which that prolific mineral is known to assume. The gangue 

 of the vein which accompanies the ore is most commonly 

 sulphate of barytes, which occurs in abundance, and in a 

 state of great purity. Calcareous spar also is common, and 

 arragonite is met with in very beautiful crystals. 



Besides galena, no fewer than nine species of lead ore oc- 

 cur in Lead Hills, some of which have not hitherto been ob- 

 served anywhere else. 



Of these nine species I may take a short review. 



1. Sulphate of lead. Beautiful specimens of this species 

 of lead ore occur at Wanlock, crystallized, and perfectly 

 white. The crystal is a right rhombic prism, and the lustre 

 is adamantine, but I think less so than that of carbonate of 

 lead. Magellan, in his English edition of Cronstedt's Mineralogy, 

 published in 1788, says, that this species was discovered by 

 Monnet, but I do not find any allusion to sulphate of lead in 

 Monnet' s Mineralogie, published in 1779; so that the dis- 

 covery of its composition must have been later than that pe- 

 riod. Klaproth first subjected this mineral to analysis in 

 1802. The specimens which he examined were from An- 

 glesey and from Wanlock Head. I analysed a specimen from 

 Wanlock Head, and found it contained no other foreign matter 

 than a trace of water. It constitutes one of the rarest of the 

 ores of lead. 



2. Carbonate of lead. This species is much more abun- 

 dant than the last. It occurs pretty frequently in crystals, 

 constituting right rhombic prisms, considerably more oblique 

 than those of the sulphates: the composition of carbonate of 

 lead ore was known to Monnet in 1779. It has the diamond 

 lustre in great perfection. This species, when made artificially, 

 is a well-known paint called white-lead. It was first analysed 

 by Klaproth in 1802. The specimen which he examined was 

 from Lead Hills ; I analysed a very fine crystal from the same 

 locality, and found it a pure carbonate of lead, with the ex- 

 ception of a mere trace of water. 



3. Cupreo-sidphale of lead. This species of lead ore was 

 first noticed by Mr. Sowerby, and so far as I know, it has 

 been hitherto met with only at Lead Hills. It has the colour 

 of the finest specimens of blue carbonate of copper. Its 

 shape approaches very nearly to that of sulphate of lead. 



Mr. Brooke analysed a few grains of it, and found it com- 

 posed of one atom sulphate of lead, one atom oxide of copper, 

 and one atom of water. By the kindness of Mr. Brown, I 

 got a specimen sufficiently large to enable me to subject it to 

 analysis: the specific gravity was 5*2137. I obtained 



