The rest of the text you quote looks important to me: "(for example, see right through a rock)."
So, I would still require the extra magnitudes for depth of penetration from The Miner's Keen Eye, if you go beyond a big rock.
That depends on how deep your spell can go (payed with extra magnitudes). If up to that depth there is something which can be just seen under the earth, then you see that. If all is dark there, your magical sense does show you nothing your normal sight would not show you anyway.
But you could also specify your magical sense differently, making it more useful, e. g. as "show me the forms of everything, that is not dirt or rock, up to a specific depth". That does not require a Requisite, if it just shows the forms like an excavation under the ashes of Pompei.
Imagine seeing into the ground: this looks like the hollow left by a corpse, this like a dagger, this like a fistful of coins - and lo, this is the relic of the fallen wooden beam that likely slew him.