206 REPORT—1863. 
inquire into the production of blende and galena in fossiliferous formations, 
we have to seek this reaction in the compounds of sulphur produced by the 
decomposition of animal matter, or in the reduction of the sulphates under the 
same influences. The hydrated silicates of zine which accompany these 
minerals prove that other forces were in action at the same time; and the 
hydrated argillaceous clays which form the metalliferous beds further attest 
these last reactions. 
The sulphides of zinc and lead, the former found in mammillated masses 
and often in transparent lamelle, have evidently been formed at the expense 
of organic matter. 
200 grammes of sulphate of zinc, dissolved in two litres of water in which 
were suspended the fleshy parts of twelve oysters, were enclosed in a bag; with 
this liquor were introduced some shells, in order to obtain the conversion of 
the sulphate of zinc into carbonate. The mixture was kept for several months, 
till putrid fermentation had ceased. The liquor no longer contained zinc ; the 
shells were partially transformed into carbonate of zinc, accompanied by 
erystals of selenite; the surface of parts of the shells had acquired a trans- 
parent rosy tint, produced by a deposit of blende permeating the shell. Left 
for some time in weak acetic acid (strong acid would decompose it), the trans- 
parent rosy tint became more developed; a part of this substance examined 
was dissolved in hydrochloric acid, with evolution of sulphide of hydrogen, 
and had the composition and characters of Blende. 
Conversion of Carbonate of Lead into Galena.—Some grammes of carbonate 
of lead recently precipitated were placed in a bag and suspended in two litres 
of water saturated with carbonic acid; putrid fermentation was kept up in 
the liquid for some months, in the manner indicated in the last experiment. 
The shells introduced into the liquid were soon covered with a metallic layer 
of sulphuret of lead. 
A weak solution of chloride of lead treated in the same way gave no 
result. 
Double Sulphate of Copper and Iron.—The double sulphate of iron and 
copper, by the reaction of carbonate of lime, and under the influence of putre- 
faction, gave, as the final result, carbonate of iron, blue carbonate of copper 
in distinct rhomboidal prisms, and semitransparent crystals of selenite. 
One of the shells, after treatment by weak acetic acid so as to uncover the 
surface, left exposed after suitable washing, and on some parts only, spots 
presenting the metallic grey and the iridescence of the sulphide of copper, 
and presenting its characters to the blowpipe. The quantity of sulphide 
found in the mixture was extremely small. The ammonia which is deve- 
loped during the fermentation must tend to decompose the sulphide of copper 
and transform it into ammoniacal sulphate. It is what takes place when 
the sulphide of copper is exposed to the vapours of sulphide of ammonium. 
The decomposition of putrescible organic matter of the nature of that 
employed in contact with sulphate of iron and earthy carbonates leads to 
different results according to the conditions in which we operate. If we 
employ a very deep vase and an abundant quantity of water, we obtain sul- 
phide of iron, free sulphur, and carbonate of the protoxide, the sulphate of 
lime which is formed remaining in the solution. If the vase, on the contrary, 
present a large surface, the sulphide of iron disappears, and the oxide of iron 
passes at the maximum of oxidation, and organic matter is consumed, In 
neither case is the iron pyrites formed, which appears to be the result of a 
slow reduction of the sulphate of sesquioxide of iron in presence of carbonates. 
