SEDIMENTARY ROCKS AND THEIR FORMATION PROCESSES Sedimentary rocks are one of the types of rocks that make up the layers of the lithosphere. They are the most abundant rocks found on the Earth’s surface. Approximately 75 percent of the Earth's surface is covered by sedimentary rocks. One of the most distinctive features of sedimentary rocks is their layered appearance. This is because they are formed through the diagenesis process of materials from other rocks that have undergone sedimentation. D