The spell description for Wall of Stone states:
It must, however, merge with and be solidly supported by existing stone.
My group was adventuring on a plain, where the ground was made of dirt. Presumably there was rock below us somewhere, but we didn’t really have any way of knowing exactly how far down that was. We were trying to make a shelter using the spells that we had, and Wall of Stone looked good, except for that one line. Our GM ended up houseruling that as long as the structure could generally support itself, it didn’t need to actually merge with stone, but I’m interested to know how other people would handle it.
In your game, do you require Wall of Stone to merge with existing stone, as the spell description states? Do you allow walls to be created on dirt, wood, or other materials? Am I just reading this description wrong?
The example given in the spell specifies that “dirt” is ok. I feel as though this line is being taken out of the context it’s written in. Here is the full context.
The wall doesn’t need to be vertical, or rest on any firm foundation. It must, however, merge with and be solidly supported by existing stone. Thus, you can use this spell to bridge a chasm or create a ramp. If you create a span greater than 20 feet in length, you must halve the size of each panel to create supports. You can crudely shape the wall to create crenelations, battlements, and so on.
As long as the stone wall is merged with and coming out of a stone from which the wall can be made, it seems that are ok. I can’t imagine that there exists a chasm which is pure stone without dirt, from which the spell is describing when it says you can create a ramp or bridge out of the wall.
As an evocation rather than a conjuration spell, it makes sense that the wall might require some stone to work with. This has been confirmed by Mike Mearls, that some sort of rock is required:
@wax_eagle : @mikemearls Can Wall of Stone be cast on dirt? It seems like its written to always need stone to merge to. Is that correct?
Mike Mearls : @wax_eagle that’s correct – need some stone to merge with or be supported by. for instance, a bridge is OK if the two ends touch stone.
Daganev : @mikemearls @wax_eagle So no stone walls on a grassy knoll?
Mike Mearls :@Daganev @wax_eagle Correct, you’d need rocks of some sort (ruins, boulders) to support it.