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a Theory of the Earth 
16. Is it well ascertained that there are certain metals 
and certain kinds of ore found only in certain kinds of 
mountains ? And, if this circumstance be true, does it 
arise from the relative age of these minerals and moun- 
tains, or from the substance of the mountains favouring 
the precipitation of one kind of mineral more than that 
of another? 
17- Is it true, as M. de Trebra says, that the richest 
veins, and the richest points of any vein, are found in the 
Tertical line which corresponds with the lowest part of 
the reservoirs of the rain water, and never in the peaks 
and most elevated ridges ? And, if this be well ascer- 
tained, would it not prove that the veins had an origin 
posterior to the grand revolutions which have given to 
the surface of our globe its present form, and that the 
metals have been deposited in them by the meteoric, 
waters ? 
18. Is it true also that the richest mines are found in 
mountains, the declivities of which are not steep ?* 
19. Are there instances of veins, entirely exhausted*, 
being again tilled up with ore ? 
20. Does the production of metals depend on the in- 
fluence of the sun and climate? Are they more fre- 
quently found near the eastern or southern, than the west- 
ern or northern faces of mountains ? 
21. Can we generalise the observation made in Sibe- 
ria, Transylvania, at Mount Hose, and in other places^ 
that in gold mines the veins are richer near the surface 
of mountains than at a greater depth ? 
21 . A. Is it generally true that the veins are richer at 
their points of intersection than in any other place ? 
22. Is the inclination of veins seen more frequently 
* As the Saxon authors generally say ; because the fact is true among them 
and in some other countries, while the case is not so elsewhere, and particular- 
ly in the Pyrenees. Til, 
