Wall of Stone: The creation of a stone wall two feet thick with a maximum length and height equalling 10 square inches. The wall will last until dispelled, broken down or battered through as a usual stone wall. Range: 6".Brendan and I discussed whether Wall of Ice should represent a conjured material that persists until it melts naturally. He contrasts it with Wall of Fire, which burns without a fuel source, so it only lasts a short while. However, the durations of Wall of Stone and Wall of Iron call this into question. The Wall of Stone can last indefinitely, but it is definitely magical and can be dispelled; the Wall of Iron only lasts a short time. It seems to me that Wall of Ice should exist somewhere between those two.
Wall of Iron: Like a Wall of Stone, but the thickness of the wall is three inches and its maximum area 5 square inches. Duration: 12 turns. Range: 6".
The differences between the Stone and Iron durations probably derive from the more natural state of the stone versus the artificial nature of the iron wall.