Do you own what is under your land?

Almog, if I buy a lot from you, do I own what is underneath it? Not automatically. The surface and the minerals can be separated, and once they are, they travel separately forever. One owner sold one half and kept the other, sometimes in the twenties or the forties. After that they travel separately, with separate heirs. How would I even check that? The county circuit clerk, the federal land office records, and the contract itself. You are hunting one sentence in an old deed. Reserving unto the grantor all oil, gas and other minerals. One line, one date. On a point two eight acre lot inside a platted addition nobody is drilling. But a seller who can't answer the question hasn't read their own chain.