125 
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- 
Proceedings— Lit. & Phil. Society— No. 3,— Session, 1861*62. 
