158 M. Daubrée on the Deposition, Composition, and 
boric minerals, without being so frequent as those of a fluoric 
nature, appear in many circumstances to have a rendezvous 
(so to speak) likewise assigned them in these same metallic 
deposits. Tourmaline, which contains nearly 6 per cent. of 
boric acid, occurs in the greater number of stanniferous masses. 
It even often happens, as at Carclaze and Mont St Michel, in 
Cornwall, at Villeder and Pyriac in France, that it is disse- 
minated in abundance through the enclosing rocks. 
Such constant occurrence of fluoric minerals in deposits of tin, 
leads M. Daubrée to suppose “that the fluorine has performed 
an important part in the formation of stanniferous masses.” 
According to him, “ this body, which has been so little attended 
to, that it has actually been passed over in silence in all de- 
scriptions of formations of tin, appears notwithstanding as ac- 
tive an agent as sulphur and the, combinations of sulphur in 
the greater portion of other kinds of metallic deposits. 
« The fluoride of tin,’ he says, “ being a fixed combination 
at all temperatures, and very volatile, we may suppose that 
this metal has come up from a depth which appears to be the 
general reservoir of metals in the state of fluorides; it is 
probably the same thing with tungsten and molybdena, the 
constant accompaniments of tin. Boron having a strong afh- 
nity for fluorine, and forming with it a combination which can- 
not be decomposed by heat, and is very volatile, one is led to 
suppose that the transport of this body has likewise taken place 
in the state of a fluoride. Finally, silicium, which abounds in 
deposits of tin in the state of Silica, combines with the fluo- 
rine in a manner analogous to the boron, and it is equally natu- 
ral to admit that a portion of the Silica has been conveyed to its 
destination under the form of a fluo-silicic acid. In support of 
the theory which he brings forward in regard to the transport 
of tin by means of fluoric acid, M. Daubrée refers to the mine 
of Huelcoath, near St Agnes Beacon, in Cornwall, where oxide 
of tin is found in the form of felspar crystals. This re- 
markable epigenie, which is so difficult to understand by the 
natural reactions between the elements of felspar and tin, is 
very easily explained when we admit that the fluoric acid has 
served both as a vehicle for the tin and as the agent which 
destroyed the felspar. 
