Earth Spell

 
Prerequisite(s): Earth Sense, Heighten Spell, Con 13+, Wis 13+.
 
Benefit: As long as you are standing on stone or unworked earth (including normal soil), you can use the Heighten Spell feat to added effect. If you cast a spell using a spell slot one level higher than the spell's actual level, the spell is treated as a spell of two levels higher and your effective caster level is increased by one. If you use a spell slot two levels higher, the spell is treated as three levels higher and your effective caster level is increased by two, and so on. You cannot gain the benefi t of this feat when casting a spell with the air, fire, or water descriptor.
 
Source: Races of Stone