Inaccurate?

Battlefield Fortification

(Heroes of Battle)

Transmutation [Earth]
Level: Sorcerer 4, Wizard 4,
Components: V, S,
Casting Time: 1 round
Range: Close (25 ft. + 5 ft./2 levels)
Area: See text
Duration: Instantaneous
Saving Throw: None
Spell Resistance: No

You shift earth to create a shallow trench or a berm, as described on page 35.
The trench or berm created is a straight line up to 5 feet long per two caster levels.
A berm created by this spell is 2 squares wide.
This spell has no effect when cast in an area of stone such as an unworked cavern floor, a flagstone floor, or a cobblestone street.