Wall of Stone

This spell creates a wall of granite rock which merges into adjoining rock surfaces if the area is sufficient to allow it. 

It is typically employed to close passages, portals, and breaches against opponents. The wall of stone is 1/4-ft thick and 20-ft square in area per level of experience of the magic-user casting the spell. Thus, a 12th level magic-user creates a wall of stone 3-ft thick and 240 square feet in surface area (a 12-ft wide and 20-ft high wall, for example, to completely close a 10-ft x 16-ft passage). 

The wall created need not be vertical nor rest upon any firm foundation (cf. wall of iron); however, it must merge with an existing stone formation. It can be used to bridge a chasm, for instance, or as a ramp. 

The wall is permanent unless destroyed by a dispel magic spell or by normal means such as breaking, chipping or a disintegrate spell. 

The material component is a small block of granite.

Any use of the wall as a bridge must be arched and buttressed. This will require 50% of the total volume of the wall, so a 20th level magic-user normally may create 400 square feet in surface area 5 feet thick. To use it as bridge, only 200 square feet can be considered, so a span 5 feet wide and 40 feet long could be made (assuming the chasm to be bridged was about 38' wide). Unsupported spans will automatically collapse of their own weight if over 20-ft across.