From the introduction:
Crumbling, Portalskippers! (That's a Dust greeting, if you hadn't guessed). Voila! just jinkled me to tell you some of the whispers on the plane of Dead Stones, the place legend has it that rocks and boulders go to when they're just too tired to carry on being so solid. It's hard work being hard, you know...
Ah, Dust and Sand. Silt and Grit. Glorious fragments of the most solid stuff. You know, some primes reckon that creatures from Dust slip into their reality at night and sprinkle dust into their eyes. What a lot of barkle, portalskippers! What self-respecting elemental creature would journey to another plane and willingly leave elemental material from its home behind? No, skippers, the real reason for sleeping dust is that the borders between the Negative Quasiplane and the Prime are decaying as the plane itself crumbles.
If you leave a room without cleaning it, dust builds up, right? That's because tiny holes between the planes let through the smallest fragments of dust and grit, see...to keep a place free of dust is a constant battle against the insidious element. Some wisebeards reckon that your prime deserts are places where the barriers grew so weak that they split asunder, allowing miles and miles of the elemental material through before they reformed again. Some say that at the heart of great deserts still lie vortices to Dust, activated by sandstorms and the like. In any case, many's the mother who's obsessively cleaned her house hoping that this would prevent a similar fate!
So what is there in the plane of Dust? Apart from the obvious (and frankly dull) endless expanses of quasielemental material, the plane has more than its share of ruins. Some chivs theorise a building that's given up the ghost and decided it's time to pass away can eventually end up here; as the bricks and mortar crumble away on the prime and the wind blows away the dust, the particles somehow end up here and continue the dying process. Only ruins that ended that way through neglect and natural wastage can make the trip, and it's certainly one way...buildings razed to the ground likewise can appear in Ash.