I know you already know about the rock cycle and types of rocks, but here is a reminder ( I had to do this or i would get a warning for attitude to learning!).
The first stage in the rock cycle is a volcano. The volcano erupts, spewing out liquid rock, or lava. Some volcanoes don't erupt, and the lava that would cool on the outside of the volcano ( extrusive ) cools under the surface of the earth ( intrusive ).
Please note that layers may differ in colour
Fast moving water brakes up bigger chunks of rock and breaks them up into sand and dust. The river or body of water will then slow, dropping the larger pieces of rock.
When the river opens up into the ocean, the current is so weak that most of the smaller particles are dropped. Over time, the sediment will be crushed down by other sediment being dropped on top of the existing layers.
Under immense pressure, the sediment will be crushed to from a sedimentary rock, such as sandstone and shale.
When the sedimentary rock gets put under giant amounts of pressure and heat, the rock morphs and turns into metamorphic rock.