DISTRIBUTION OF METALLIC VEINS AND MINERAL BEDS, &C. 49 
13. Gold, tellurium, antimony, and manganese, extend from 
the newer primitive to the older secondary. 
14. Lead, zinc, catlmium, and mercury, though sometimes 
found (especially lead) in the older rocks, appear to be the most 
recent of the metals, occurring in the greatest quantity in the later 
transition formations. 
15. Iron is found in every rock, from the oldest gneiss or 
granite to the most recent alluvial deposit. 
16. A number of different metals are frequently associated, or 
occur in considerable quantities at moderate distances, within the 
limits of the same mining district. The tin, copper, lead, gold, 
silver, iron, bismuth, zinc, antimony, cobalt, arsenic, tungsten, 
titanium, nickel, manganese, and molybdenum (16), of Corn- 
wall — the silver, iron, arsenic, copper, lead, zinc, gold, tin, 
quicksilver, antimony, and manganese, (11), of the great silver 
mine at Guanaxuato, in Mexico — the gold, silver, copper, lead, 
arsenic, and iron, of the mining region of North Carolina, are 
examples. 
17. A rock of a given character will be eminently metalliferous 
in one country, and in another where its apparent age, structure, 
composition, and other characters are much the same, it will be 
almost without the trace of a metal. The gneiss of Saxony is 
rich, that of Scotland is poor. This diversity we are unable to 
account for. From the general aspect of a country, therefore, 
we can form only some very loose conjectures respecting its rocks, 
whether they will be metalliferous or not. 
29. The foregoing statements comprise the principal facts 
that have been ascertained, respecting mineral veins and beds in 
general. They relate especially, to the primitive, transition, and 
older secondary rocks, to which, as has been remarked, metallic 
veins are confined. Three substances of great importance and 
value, either in the domestic economy of mankind or in various 
arts and manufactures, are found in greatest abundance amongst 
the secondary strata, the geological position of which, and the 
circumstances under which they occur, will be stated somewhat 
at length, both because the subject is interesting in itself, and 
because the facts to be noticed afford some insight into the 
ancient condition of the earth, and enable us to comprehend the 
nature of the revolutions to which it has been subjected. The 
substances referred to, are fossil salt, gypsum, and coal, with 
which last, iron ore is often associated. 
For the study of the secondary strata, no country whose geo- 
logy has been hitherto investigated, offers as many advantages as 
England. Nearly the whole of the south-eastern and midland 
counties are underlain or constituted of formations belonging to 
this period, disposed in successive beds one over the other in a 
conformable position and dipping very gently towards the south- 
east. The space they occupy on the earth's surface, is not so 
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