PAIN.] PROCESS OB' CONCENTRATION. 67 



that the waters Avere loaded before reaching these horizons rather 

 than the reverse, and wonld make the association of the flnorspar 

 with the Ste. Genevieve a matter dependent npon the precipitating 

 action of the latter rather than the reverse. This does not exclude 

 the possibility of minor contributions to the veins from the surround- 

 ing country rock, though it may be pointed out that it is to the 

 lower-lying Cambrian, Ordovician. and Silurian rocks that one 

 w^ould look for any considerable quantity of lead and zinc if the 

 general analogy of the other districts in the Mississippi Valley be 

 considered important. This was indicated in an earlier general 

 paper on the lead and zinc deposits of the valley." The published 

 data then available prove to have been somewhat misleading, and the 

 analogy is now believed to be less close than was suggested. 



It is probable that the unusual (|uantity of apatite in the dike 

 material, and to a less extent the large micas, indicate a magma in 

 which fluorine was present, and that this fluorine was given off to 

 the underground waters during the period of cooling and consolida- 

 tion of the underlying mass of rock. 



The association of the minerals and the common phenomena of 

 marked silicification of the hanging wall are interpreted as indicating 

 deposition from heated ascending solutions carrying fluosilicates 

 of zinc, lead, copper, iron, barium, and calcium. These are be- 

 lieved to have been broken up and precipitated by descending cold 

 waters, which possibly also furnished the sulphur to combine Avith 

 the metals, though it is not improbable that sulphur Avas an original 

 constituent of the rising solutions. 



eco:nomic importa:n^ct] axd future of the district. 



S0URC;ES AMD USES OF FLUORSPAR. 



The Kentucky-Illinois district is not only the main American 

 source of fluorspar, but is the only one from Avhich spar reaches the 

 general market. Since 1882 the district has produced 260,000 tons 

 of spar, having a total value of $1,521,020. 



There are no data for determining the production of the Illinois 

 mines separately. For many years they produced practical!}' all the 

 output. Recently the Kentucky mines have been developed, and 

 noAV are jDroducing more than those north of the Ohio. In the folloAV- 

 ing table are given the output and value of fluorspar in the United 

 States for 1902 and 11)03, the figures being taken from Mineral 

 Resources of the United States, 1903. 



"Van Hise, C. R., and Bain, IT. Foster, Lead and Zinc Deposits of the Mississippi ^^'ll 

 ley, U. S. A., read before tiie Institution of Mining Engineers, London, 1902. 



