342 
MINERALS. 
6. A second layer of loadstone of 130 feet in 
thickness. 
7- A third calcareous bed like the second, but 
double the thickness. 
8. A third layer of toadstone, like the two others, 
66 feet in thickness. 
9. A fourth bed of calcareous matter, which has 
been penetrated 200 feet without reaching the bot- 
tom. 
The veins which run in these different beds 
pursue a very regular course, and are from three 
to twenty feet thick. They run either in a per- 
pendicular, or oblique direction ; a very few are hori T 
zontal. It is remarked that the nature of the veins 
change according to the beds through which they 
pass, and that they disappear entirely in the toad- 
stone. The veins in the beds of sandstone and slate 
are without metal : in the four calcareous layers, on 
the contrary, they are always very rich, but the 
mineral constantly disappears when cut off by the 
beds of toadstone ; though, notwithstanding this in- 
terruption, it appears again and continues its course 
in the calcareous layers. 
•/ 
The various layers of earth which are seen as 
men descend into a mine, differ in their quality in 
different parts of the world, but all show in some 
of their strata the particular metal for which the 
mine has been dug. Gold, silver, copper, tin, lead, 
iron, and every other metallic substance which we 
meet with in the bowels of the earth, has a very 
