[Skarg]

I would also point out, that if you DO rule as hcobb suggests, that an earth elemental can pass through earth as if it were insubstantial... well that means that almost everyplace, it could just shift DOWN through the ground and become more or less invulnerable, and it'd also be easy for it to go extremely deep underground. You'd almost never have more than one turn to try to catch an earth elemental that wanted to escape, and they could stalk you underground and appear behind you with no warning, etc.