Road base, a mixture of dirt and gravel, varies in composition depending on location. Some types pack very hard while others remain loose and dusty. It makes a good base for almost any kind of solid flooring. Gravel comes in various sizes. It drains extremely well and makes an good base for many types of solid flooring.
Sharp gravel makes a more stable base than round gravel.
Like sand, gravel is unstable and usually dusty, so is unsuitable as a finished floor. Wood performs best when installed over a base that drains, such as road base, limestone or gravel, so it is not in constant contact with moisture. Properly installed it will remain stable and level. Even untreated wood, if not contacting the earth, can last for 30 years or more. A wood floor can be very slippery when wet.