1. The order in which sedimentary layers are deposited, the highest being the youngest.

2. The process by which the layering occurs.

The principle of superposition states that any given geometric figure in a euclidean space can be so moved about as not to change its size or shape.

Addition of phenomena when the sum of two physically realizable disturbances is also physically realizable; for example, sound waves are superposable in this sense, but shock waves are not.