You create a wall of faintly shimmering elemental energy. Upon casting the spell, choose either acid, cold, electricity, or fire. The spell gains the chosen descriptor, and any thrown weapons or ammunition that pass through the _augmenting wall_ as part of a ranged attack deal 1d6 points of energy damage of the specified type in addition to their normal damage. The wall has no effect on melee weapons or items not thrown as part of an attack. As you cast the spell, you can limit the wall so that it only affects ranged weapons passing through it in the direction of your choice. Doing so halves the spell’s duration.