When a flooding river flows over a levee and into the floodplain, the competence of the flow decreases. One of the main sources of acid rain is smoke from coal-burning power plants. The oil then migrates towards the surface. If it is trapped along the way, an accumulation of oil is formed. The earth is not truly spherical, but is compressed at the poles and distended at the equator.
Oceanic crust is thicker than continental crust and is made of basalt.
Ripple marks, mud cracks, and cross-beds are all good examples of sedimentary structures.