Not quite. 35 million years ago the Upper Rhine Plain was a mountain range from Basel to Frankfurt. Then the middle fell down due to stress and stuff, i.e. that’s the plain. On either side the hills remained, forming the Odenwald and further south the Black Forest, and on the other side of the Rhine, the Pfälzer Wald and the Vosges in France. That’s why you have a plain and then a rapid ascent (only to about 400m in our area, higher if you venture south). The stone is porphyry, hence the quarry.
pictures imperfect blog 
An extinct volcano?
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Not quite. 35 million years ago the Upper Rhine Plain was a mountain range from Basel to Frankfurt. Then the middle fell down due to stress and stuff, i.e. that’s the plain. On either side the hills remained, forming the Odenwald and further south the Black Forest, and on the other side of the Rhine, the Pfälzer Wald and the Vosges in France. That’s why you have a plain and then a rapid ascent (only to about 400m in our area, higher if you venture south). The stone is porphyry, hence the quarry.
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Ah, OK! Thanks for the explanation
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