VI. — On Ancient and Modern Tin-works in France. — From Mr. 

 S. E. Pattison. 



N the southern portion of central France, there occurs a con- 

 siderable area of primary rocks, pierced by the volcanic 

 deposits of Auvergne. On the north-west edge of the granitic 

 plateau, in the district of the Limousin, there are scattered tin- 

 works, both mines and stream-works, which are similar, in the 

 mode of their occurrence, to those of Cornwall. A description of 

 these stanniferous localities by M. Mallard, in the last number of 

 the Annates cles Mines,^ enables me to furnish some particulars 

 illustrative of their mineralogy and archseology. 



There are two leading varieties of granite in the district re- 

 ferred to : one in which all the mica is black, the more ancient 

 of the two ; the other containing both black and white mica. 

 Both have the characteristics of erupted rock. On, or rather 

 against them, lie, in succession, crystalline schists, gneiss, and 

 mica-slate ; and over' all, a mantle of tertiary clay, frequently 

 worn through to the foundation rock. The mineral veins extend 

 both through the granites and the schists, and are clearly pos- 

 terior to both. The metallic crystals in the vein stuff are usually 

 found near the sides of the lode ; the walls of the lode, when in 

 the granite, are much altered, the felspar being replaced by clay. 

 The vein stviff contains wolfram, tin, mispickel, arseniate of iron, 

 native copper, uranite, fluor sj)ar, rarely phosphate of lime, and 

 sulphate of barytes, and lastly, and most sparingly of all, gold. 



The stream gravel overlies the nigro-micaceous granite. It 

 attains, in some places, a thickness of several feet. Its base is a 

 thin bed of clay, which parts it from the granite. The gravel is 

 sandy, the upper part is of no value, the lower portion is treated 

 for tin, and in this is found some grains of gold. The deposit is 

 overlaid by peat containing trunks of trees. 



* Annales des Mines. Sixihne Serie. 5 Livraison de 1866. Note sur 

 les Gisements stanniferes du Limousin et de la Marche, dx., par M. Mallard, 

 ingemeur des mines. 



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