Igneous layers are a given at volcanoes, I've yet to see a volcano without at least 4 layers of igneous rock listed. You're aware of what igneous rock is right? It's solidified magma
Right. What are you trying to explain?
Like I said, you need Metamorphic at the same embark as Igneous. With the scarcity of Volcanoes, this could be tough, could it not?
So you need both a Metamorphic layer and an Igneous layer at a Volcano? Isn't this sort of hard to find on a 'normal', non-fiddled world?
That's what I was responding to, your apparent confusion in thinking that igneous rock is hard to find at a volcano. On a non-volcanic embark, it is much less likely that you'd have igneous layers and much more likely that you'd have sediment layers, making the point moot.
In case the confusion was over Metamorphic layers, those are
everywhere, metamorphic layers are the ones that are deep into the earth, even if the embark location didn't list marble as one of its layers, you have a good chance of finding some if you dig deep enough.
I think a real challenge would be to make a workable base at a location that is volcanic enough to have igneous rock instead of sedimentary rock, but doesn't actually have a volcano. Much harder to get fuel in this case.