The dream world is not actually a world consisting of soil, earth and rocks, they are living worlds or rather beings.
Sometimes there is an intergrowth from a world like a dandelion here on earth, it gets bigger and bigger, that depends on the number of dreams.
They grow so big that at some point they break off and are slowly carried by the wind.
They are seedlings and they can float through the air for thousands of years, sometimes they end up on another world and sometimes they float and are populated by other dream beings.
This creates new dreams and dream worlds.