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Deposition is the process by which wind or water sediment settles out in layers. Furthermore, over time, the remains of living things may harden in this sediment and change into fossils. After sediment is deposited the processes of compaction and cementation change the fragments into sedimentary rock. Compaction. At first, the fragments of rock lie loosely together. But gradually, over many, many years these thick layers build up. This build up becomes heavy and presses down on the layers beneath it. Compaction is the pressing down of layers forcing the sediments to fit closer together. Over millions of years, this process can squeeze fragments tightly together. The layers often remain visible in the rock and may be used to identify sedimentary rock. Cementation
Hydration-This type of weathering occurs when rocks absorb water, and the resulting hydrogen and hydrate ions form new bonds with minerals present within the rock. This type of chemical erosion can actually result in a change to a new form of rock, such as the process by which gypsum is formed.hemical erosion, also called chemical weathering, causes the breakdown and decay or rocks or other geological features through a chemical process. This process can be the result of manmade activity, or the chemical composition of soil or water as it moves across the rock's surface.