Hidden Landscapes

Agricola describes, and sketches, many types and configurations of ore deposits beneath the earth's surface. Venae profundae (deep veins), venae dilatatae (spread-out veins) and venae cumulatae (not really veins at all, but accumulations, like a lake). There are many variations and combinations. For example, veins might bend, or slope more or less, extend from one mountain to the next or from a mountain to a plain, cross, join, or diverge. His pictures show how to visualize while on the surface of the earth, the veins that lie beneath it.

Agricola doesn't miss the resemblance of ore deposits to water formations (lakes and rivers), and he makes the hypothesis that ore deposits formed from "juices" flowing under the earth, like the underground water with which he was also familiar. These juices were solutions of metallic compounds, which formed crystals or deposits over time.

Besides being useful for knowing how and where to dig, this hypothesis is exciting, according to Hoover, in a couple of ways. First, though not "set out with the clarity of Darwin," it represented a leap from the simplistic Genesis thinking that prevailed at that time, to understand that the earth was not formed as it is today, all at one time. Rather, the rocks seem to have formed first and the ore-deposits later. One of Agricola's examples shows what happens when two veins form at different time and they cross, and he explains the resulting formation in terms of geologic change. Another sketch may show the effect of plate tectonics on an existing vein.

A more subtle point has to do with the nature and specialness of metals (and here the footnotes get much longer than the text). The ancients knew that metal was special stuff with special properties, but they weren't sure why. Some of the ancient Greeks saw metal as being related to water - it's shiny, it's liquid at some achievable temperature, and it seems to absorb cold. Alchemists, respected in Agricola's time, considered metal to have almost magical or mystical properties related to heavenly bodies. More practically speaking, metal is very useful and you can't find it just anywhere. A nation or individual lucky enough to have ore deposits on their land can become very wealthy; this could lead to believing that different parts of the earth have inherently more value than others.

It's maybe more true, and maybe a more democratic view to emphasize that metal like everything else is composed of atoms, metals being elements with special properties, but still elements like all the other stuff around us.