The diagrams illustrate the process of forming sedimentary rock in coastal areas.
The first two diagrams depict how the boulders, made as the result of mountain cracking, slide down right to the river water. Afterwards, these stones swim downstream until they get to the lowest water level.
The last two diagrams show the process of forming the sedimentary rock. As the consequence of erosion, huge stones become much smaller as well as transform into the pebble. Initially, this pebble settle evenly under the water level, where it mixes with other materials like sand and cement. Due to high and low tides, in time this sediment accumulates closer to the mountain base – the lowest part of the mountain, and creates the coasts. Additionally, coast comprise a plethora of sediment levels: from big rocks to the tiny pebble.
Overall, the process of forming sedimentary rock consists of two stages. Firstly, boulders are formed as the result of fissures. Then they move to the base of the mountain. Secondly, these stones transform and mix with other materials.