Which process is most likely responsible for the removal of the missing parts of the rock layers

I believe Erosion is the process most likely responsible for the removal of the missing parts of the rock layers. Erosion involves the physical action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, then  moved away to another location. 

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.