366 On Mineral Melamorphism. 



from the external, nearly copperless exterior. In South 

 America, gold, containing silver, is reduced to almost pure 

 gold, when the grains are nealed with brick-dust and culi- 

 nary salt ; the silica, assisted by the watery vapours issuing 

 from the fuel, decomposes the muriate of soda, when muria- 

 tic acid is evolved, and the chlorine unites with the silver 

 to form chloride of silver. In more recent times, there have 

 been produced, by direct smelting experiments, or as casual 

 pi'oductions of the forge, many minerals which most frequently 

 belong to the volcanic and metamorphic rocks. Augite, a 

 principal ingredient of many lavas and ti'aps, was discover- 

 ed in the slags of Fahlun. The slags of Sahla are decep- 

 tively like basalts, and their cavities are occupied by augite 

 crystals. By fusion of the ingredients of augite, Berthier and 

 Mitscherlich obtained distinct crystals of augite. A mineral 

 isomorphic with olivin, a common ingredient of basalt, is not 

 unfrequently contained in the slags of the iron-refining and 

 copper-smelting processes. Felspar was found in the shape 

 of distinct crystals, possibly formed from vapours (Hausraann) 

 in the rents of a copper-furnace at Sangershansen, in the dis- 

 trict of Mansfeld. At Stolberg, on the Hartz Mountains, 

 small twin crystals, exactly similar to the adularia of Mont 

 Gotthard, were found in a deserted iron-furnace 5f feet 

 above the floor (Hausmann). A direct formation of felspar 

 lias never yet been obtained by the fusing together of its in- 

 gredients. Mitscherlich met with mica in the form of hexa- 

 gonal prisms, in the old slags of a copper-melting furnace in 

 Sweden. Hausmann met with scales nearly related to mica, 

 in the cells of a crystalline sandstone which had served in 

 the Hartz as the floor or bottom of an iron-furnace. Garnets 

 and Idocrases have partly been produced from their ingredients 

 by smelting, and have partly been found in the slags of fui'- 

 naces. A crystalline substance, resembling the mineral 

 named "VVollastonite, was discovered in iron slags. Gaudin 

 made crystals of corundum by artificial means. The meta- 

 morphosis of many rocks, which have been mentioned as ab- 

 normal or older limestones, clays, sandstones, and coals, rests 

 on these facts and others yet to be quoted ; although, in 

 many cases, we should be at a losp to explain the act of me- 



