Is there an earthquake spell in the game? (I didn't play earth mage yet) It could do earth damage, but I like it better your way, Stabbey, so earthquake could do no damage (or physical) just stun all who fail the saving throws, or even destroy some crates/barrels, which can be handy. Otherwise I cannot think any other earth spell which would do earth damage. Since earth is connected to fire, there could be some earth spells doing fire damage, or so..
