"People should be warned it’s quite difficult to read Humboldt on this matter, because he will spend 15 pages on the obsidian ***"
What does this old man say? ...obsidian and what?
Your answer will be appreciated.
I think he says "obsidian and ... um ... porphyry". That is how it sounds to me and the word does make sense in connection with obsidian.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.
Thank you all. Thank you for the answer.