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Ordinary Meeting, October 29 th, 1861. 



• J. P. Joule, LL.D., President, in the Chair. 



Professor A. D. Bache, Superintendent of the United 

 States Coast Survey, and Commander M. F. Maury, of the 

 United States Navy, were elected Corresponding Members 

 of the Society. 



John Edward Morgan, Esq., M.B., was elected an 

 Ordinary Member. 



Mr. Spence brought before the meeting part of a mass of 

 iron and copper pyrites, containing abundance of large and 

 well defined crystals of pure arsenious acid. 



Not only are these crystals a novelty as a natural product, 

 but as an instance of rapid mineralisation they are interesting. 

 The lump was found among a cargo of small disintegrated ore 

 imported from Huelva, in Spain, and containing no solid 

 masses of large size, and the lump was merely an aggregation 

 of small pieces firmly agglutinated together and full of hollow 

 cavities, studded over with the crystals of arsenious acid ; and 

 from the history of the cargo of ore it is not probable that 

 more than twelve months has been required for their develop- 

 ment. Heat does not seem to have been the cause of the 

 metamorphosis, as there is no evidence of heat at all approach- 

 ing to ignition having occurred ; discoloration of the ore would 

 at once have been the result of this. 



The ore is chiefly a sulphide of iron and copper ; but as an 

 arsenide of one or both of these metals exists in it, decom- 

 PftOCEEDiNGS— Lit. & Phil. Society— No. o.—Sessiox, 1861-62. 



