The Inner Planes ain't as pure as a Basher might think. They have pockets of other elements scattered about them, what with one thing or another. On the Plane+of+Air, pockets of earth give you a place to stand, while on the Plane+of+Earth, pockets of air give you a place to breathe and move around in. Pockets of water can give you something to drink on an otherwise moistureless plane, while a pocket of Vacuum can give you a good opportunity to unexpectedly asphyxiate - not all elemental pockets are good things, Berk!
Some elemental pockets are more or less pure, but others are mixed with the surrounding element, so a pocket of water on the Plane of Earth can be more of a muddy puddle.
Source: The Inner Planes, pages 13-16
- 396 reads