In Africa and parts of Asia and South America, laterite soils are used to build dirt roads. However laterite, called "murram" in East Africa, varies considerably in the proportion of stones (which are usually very small) to earth and sand. It ranges from a hard gravel to a softer earth embedded with small stones. Not all laterite and murram roads are therefore strictly gravel roads. Laterite and murram which contains a significant proportion of clay becomes very slippery when wet, and in the rainy season, it may be difficult even for four-wheel drive vehicles to avoid slipping off very roads into the drainage ditches at the side of the road. As it dries out, such laterite can become very hard, like sun-dried bricks.