In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Dirt
If you are in a dirty environment or are dirty yourself then expect plenty of financial gain. If you are treading on dirt be careful with your movements as you could make a mistake and cause damage that will be disruptive.