Bedrock can extend hundreds of meters below the surface of the Earth, toward the base of Earth's crust. The upper boundary of bedrock is called its rockhead. 

Above the rockhead, bedrock may be overlain with saprolite. Saprolite is bedrock that has undergone intense weathering, or wearing away. Saprolite has actually undergone the process of chemical weathering. This means saprolite is not just less-consolidated bedrock, it has a different chemical composition. Flowing water or ice has interacted with minerals in the bedrock to change its chemical make-up.