Another major rock group is a Sedimentary rock. Sedimentary rocks form through Deposition, Compaction, and Cementation. In The first step Erosion takes place. Erosion is when rocks wear away from wind, water, ice, heat, cold, rain, waves etc. The forces of the Erosion form sediments and the rock fragments are carried away by water or wind. The second step Deposition, the rock fragments are carried by the water or wind. In Deposition, the rocks settle down and slowing come out of the water. The third step Compaction, The process presses the sediments together. Over millions of years the rocks build up creating layers of rock. Cementation, the final step, is when the rocks slowly dissolve and particles and spaces seep into the rocks, forming Sedimentary rocks. There are also three groups of Sedimentary rocks, Clastic, Organic, and Chemical rocks. Clastic rocks form from the particles of other rocks. Some Clastic rocks contain a mixture of rock fragments of all sizes. Organic rocks have to have something that was once living in them. Leaves, animals, plants, anything. The last kind of sedimentary rock is Chemical. Chemical rocks are formed when solutions crystallize. Chemical rocks can also form from mineral deposits left when sea levels evaporate. Also these rocks have many uses. Some of them are used for building, glass, chalk, roads, and bases.