3$Q Hints for the Formation of 
contrary, tlian parallel to, tlie adjacent face of the moun- 
tain ? 
23. Does it sometimes happen that the rock which 
forms the sides ( nehen-gestein ) of the vein is as rich and 
even richer in metal than the vein itself ; and would it 
thence follow, that the metal arrives at the vein by filter- 
ing itself through these sides ? 
2-1. Is it true that, in 'mountains of granite, the grain 
of the granite is finer and the stone more tender in the 
neighbourhood of a vein ? 
25. Are there observed in any mine proofs that sub- 
terranean fires have contributed to its formation by sub- 
liming the metallic substances, or by melting them ? In 
a word, are there seen there any traces of the action of fire? 
26. In the greater part of mines do we not, on the 
contrary, observe proofs of the action of water in the si- 
tuation of minerals and of their matrices ; in their druses 
(groups of crystals), and in the state, form, and nature of 
their crystallisation ? 
27. Does there prevail, at the bottom of mines, a heat 
superior to the mean temperature of the earth ? And if 
such a heat exists in any mine, may it not be explained 
by that produced by the lamps ; by the miners them- 
selves ; by some accumulations of pyrites* or some local 
reservoirs of water, without having recourse to a gene- 
ral cause or central fire ? 
28. Is it certain that, in general, veins decrease in 
thickness in proportion as they proceed to a greater 
depth, and terminate in such a manner that the fissures 
which contain them are closed at the bottom? Were this 
fact established, would it destroy the possibility of subli- 
mations arising from the interior parts of the earth ?* 
* 28. A. I)o there exist veins of from ten to twenty fathoms and more in 
thickness ? or have not metalliferous banks or fissures between two different 
kinds of stone been taken tor veins ? Til 
