292 Transactions of the Geological Society of France. 
phuret in consequence of the developement of an electro-chemical 
action. The contact of the lead with the chloride produces a double 
chloride, the magnesium is momentarily set at liberty, the lead be- 
comes electro-negative and the solution electro-positive ; the first al- 
ters the sulphuret of mercury, while the sulphur which is electro- 
negative goes to the double chloride. A portion of sulphur combines 
with the lead of the double chloride and gives rise to a sulphuret, 
whilst another portion combines with the chloride of magnesium 
forms a sulpho-chloride. ‘The artificial sulphuret of lead crys- 
tallizes in regular tetrahedrons, which is a form comprised within 
the system of crystallization of the cube, as well as of the octahe- 
dron. 
M. Brqueret obtained in the same way, analogous results with 
sulphuret of antimony, zinc and iron. 
Geologists must be happy to find this distinguished chemist, apply- 
ing his knowledge of electro-chemistry, to the study of the altera- 
tions which daily take place on the surface of the earth as well as 
within its interior. In his first memoir on this subject he is occupied 
with the formation of carbonate of lead upon plates of that metal 
‘subjected to the action of carbonic acid coming from the decomposi- 
tion of wood. In this case, the energy of the action of the acid was 
augmented by the contact of the metal with a wood already decom- 
posed, and influencing the circulation of the electric fluid. 
He has also examined the formation of the phosphate of iron, 
crystallized in the midst of an accumulation of vegetables, of bones 
and of fragments of gneiss; and has been led to observe that the 
crystals were placed upon fragments of carbonised wood, that is, on 
the best conductors for reproducing gradually, the neutral fluid, dur- 
ing the continual disengagement of the two electricities, which takes 
place in the mutual reaction of the different portions of the mixture. 
He also remarked, between the layers of the gneiss, phosphate of 
iron formed at the expense of the iron in the mica, through the ac- 
tion of the solutions containing other phosphates; the result of the 
operation was a mica destitute of color. 
GEOLOGY. 
Origin of Nitre—The theory of the origin of Nitre is a ques- 
tion of considerable interest to the geologist, not only in itself, but in 
its connexion with the origin of various other saline substances. M. 
Gautier DE Cuiausry has described the operation of nitrification, 
