Or more accurately, a short story from a book. It's science fiction, possibly fairly old ('60s onward), and I remember reading "Soldier from Tomorrow" (http://en.wikipedia.org/wiki/Soldier_(The_Outer_Limits)) in a related book, might have been Outer Limits or something similar.
I'm vague on the story but along these lines: two characters from two different races find themselves on a rather large patch of sand. They are separated by an invisible wall, which only permits non-organic material (e.g. rocks) to pass it. The two must fight for survival, against each other. It could have been that their civilisations were at stake, maybe.
I'm vague on the story but along these lines: two characters from two different races find themselves on a rather large patch of sand. They are separated by an invisible wall, which only permits non-organic material (e.g. rocks) to pass it. The two must fight for survival, against each other. It could have been that their civilisations were at stake, maybe.