L^: d5, mu5	-	R#: 16" (mu: 1" per level)	-	D^: S
C^: v.s.m (mu: v.s.m)	-	CT: 7  (mu: 5)	-	S^: None
A^: (2" cube)*  (mu: 2 cubic " /level)	MP: 25	-	Transform element to negative quasi-element: MP.28	Transform element to para-element: MP.28
Players Handbook	-	-	-	AD&&D

Effect: This spell turns natural rock of any sort into an =equal= volume of mud.

The depth of the mud can never exceed one-half its length and/or breadth.
If it is cast upon a rock, for example, the rock affected will collapse into mud.
Creatures unable to levitate, fly, or otherwise free themselves from the mud will sink and suffocate,
save for lightweight creatures which could normally pass across such ground.
The mud will remain until a dispel magic spell or a reverse of this spell, mud to rock, restores its substance --
but not necessarily its form.
Evaporation will turn the mud to normal dirt, from 1 to 6 days per cubic 1" being required.
The exact time depends on exposure to sun, wind and normal drainage.

MC.magicuser: Except as noted above, and that the material components for the spell are clay and water
 this spell is the same as the fifth level druid spell, transmute rock to mud.

DMG: Rate of sinking is 1‘ per segment,
    i.e. 1‘ per 6 seconds or 10 ’ per minute (round).
Brush thrown upon the surface will stop sinking of creatures able to climb atop it
(use discretion as to the amount of brush and the weight of creatures).
Ropes can be used to pull creatures out of the mire, assuming that sufficient power is available --
1 man/man, 10 men/horse (or vice versa).

Transmute Mud to Rock: The mud to rock reverse will harden normal mud into soft stone (sandstone or similar mineral)
permanently unless magically changed.
The mud [from a Transmute Rock to Mud] will remain until a dispel magic spell or a reverse of this spell, mud to rock,
restores its substance -- but not necessarily its form.

Transmute Mud to Rock.MC.magic-user: sand, lime, & water.

NOTES BY GARY GYGAX
<link to full version>

I avoid the whole issue by ruling that the rock is turned into nonmagical mud (hence not subject to Dispel)... i.e. that the process is magical but the resulting material is not.
- Frank Mentzer
 

Ciao!

As a matter of fact I did not allow a wall spell to be cast save if there was some surface the bottom edge it could rest upon.

If you allow them to be cast into the blue, then MR will not affect one in falling, as it is not a spell.
MR does not affect blosw from magic wea[ons, eh?
The same goes for rock turned to mud.

Cheers,
Gary
 

And you have come to the right person for a frivolous answer 
 

My players know better than to try something sure to incur wrath <devious>

Such tactics are a matter for the DM to manage, and as one here is how I would handle an attempt of this sort.

"Sorry, Flubspell, but your Rock to Mud casting seems to fizzle out when it contacts the stonework of the temple. golly, I guess the builders must have imbued it with some fort of protection from this sort of assault on its integrity..."

"Oh, by the by, it seems that you are now turning a ghastly gray color. It seems as if yout attempt has invoked a curse of some sort, as you feel quite weak and not at all well..."

I'd use the same sort of response if someone tried that with any important campaign setting. To stop the rules lawyers from their shrill protests I's write up a few spells to cover constructions--anti-disintigration, anti-rock to mud, etc. Also a few retributive spells to be activated and aimed unerringly at any spell caster attempting to bring down a stricture by that sort or obvious and predicatble tactic. Just because such spells are not included in the standard roster doesn't mean they don't exist.

Cheers,
Gary
 

Heh, and I wasn't pointing a finger and fault-fnding. My players try all sorts of imaginative and generally underhanded tactics, and so do I when I am playing, not GMing 
 

Why allow the players to mess up the campaig setting?