Sometimes the footing can go deeper than the building is tall above-ground.
So I've been told. Houston, TX for example doesn't have bedrock. It's effectively dried up swampland. What we have is "gumbo clay". I've also been told that one of the reasons we don't have a subway is because of the unstable nature of the ground and the constant need to pump water out. In fact, we have an entire industry here that repairs residential home foundations. It's just a fact of life here.