Origin of Masses of Tin Ore. 155 
covered in the grand laws which have regulated the formation 
of the earth, the history of metallic beds is at least fully 
known. Such, however, is by no means the case, and the 
mineral kingdom presents us with the singular circumstance, 
which has already been remarked, that the phenomena least 
known are almost always those which we are in a condition to 
observe every day. Indeed, if we read the numerous descrip- 
tions which have been published on mineral deposits, we re- 
mark differences which may well excite surprise. This is 
often owing, in part, to the observations having been made on 
a small scale, and to the circumstance of particular cases or 
exceptions having been too frequently mistaken for general 
laws. In this respect, M. Daubrée’s Memoir is of great in- 
terest. He has visited the greater number of tin mines in 
Europe ; and the remarkable conclusions he draws from their 
comparison, with respect to the origin of these metalliferous 
beds, deserve the full attention of geologists and chemists. Be- 
fore giving an account of them, we think we should state the 
principal circumstances mentioned by this young professor. 
Tin mines are disposed to assume two kinds of arrange- 
ment, which are carefully distinguished by the miner; some 
form very circumscribed masses ; others, on the contrary, con- 
stitute veins of small width, but often of considerable extent. 
It will be understood, by these words alone, how different the 
modes of working them must necessarily be; in the one case 
the works, included in a very small space, are merely required 
to raise the bed in a mass; in the other they are placed at 
some distance from each other, and form a long train. These 
differences in form are almost always accompanied with still 
greater differences in the disposition of the mineral; in the 
case of the arrangement in masses, the oxydized tin composes 
very slender veins, which, taken together, form a net-work dif- 
fused in an almost uniform manner throughout the rock, in 
such a way as to appear contemporaneous with it. 
This arrangement is observed in the mass of Geyer, in 
Saxony, where the oxide of tin is disseminated throughout the 
matrix in fine particles, often imperceptible to the naked eye. 
In mines where the tin occurs in veins, the metalliferous 
part is, on the contrary, completely distinct from the enclosing 
