﻿Yol. 66.~] IN THE LEAD AND ZINC VEINS OF GEEAT BRITAIN. 



301 



Bock. 



Local 'it y. Lead. 



Zinc. 



Granite 



Granite 



Granite 



1 Per cent. 

 Foxdale. -004 

 Threlkeld. -003 

 Glendalougb. -004 

 Dartmoor. *002 

 Eotberbope. -003 

 Darlevdale. "001 

 Conway. "0025 

 Greenside. -006 

 Leadhills. -001 

 Halkyn. '0005 

 Matlock. -001 

 Alston. -0015 



Per cent. 

 •005 



•on 



•001 



•002 



•0005 



•001 

 not found. 



•002 

 not found. 



•0015 



•0005 



•001 



Granite 



Diabase (Whin Sill) 



Diabase (Toadstone) 



Volcanic asb 





Slate 







Limestone 



The results were verified as far as possible by blank experiments, 

 and by tests of the reagents used : while some duplicate analyses 

 made indicated that the figures were generally correct to within 

 30 per cent, of the amount stated. The results correspond with 

 those of W. F. Hillebrand on the Leadville porphyries, where the 

 average amount of lead oxide was determined to be 0*002 per cent. 1 

 Similarly, J. D. Robertson, in the Archaean rocks of Missouri, records 

 0*004 per cent, of lead and 0*009 per cent, of zinc. 2 The foregoing 

 analyses, like those of Luther Wagoner for gold and silver in rocks 

 at San Francisco, 3 show a higher percentage of metals in the igneous 

 than in the sedimentary rocks, suggesting the conclusion that the- 

 metals in the latter rocks have been derived by denudation of the 

 older igneous and crystalline rocks. 



A consideration of the areas which were basins of deposition in 

 Britain during the Carboniferous Limestone epoch shows that these 

 basins received the drainage from the older rocks, and gives some 

 ground for the belief that the traces of metals found in the lime- 

 stones by analysis have been derived from the older rocks and 

 deposited contemporaneously with the limestones. Thence, it is 

 only a step to assume that the ores of the veins have been concen- 

 trated by circulating waters from the disseminated metals in the 

 limestones. There are several objections to this view, and these 

 may be tabulated as follows : — 



(1) Analyses were made of specimens of limestone from the 

 Yieille Montagne Company's mine at Nenthead. The specimens 

 were taken along a cross-cut, at varying distances from the vein 

 and along one and the same stratum — the Great Limestone. The 

 results were as follows : — 



1 Loc. supra, cit. 2 Loc. supra, cit. 



3 Trans. Amer. Inst. Min. Eng. vol. xxxi (1901) p. 808. 



