Simplify the following text for a Grade 15 native English-speaking person.
Original: The theoretical basis for the subject was established by Nicholas Steno who re-introduced the law of superposition and introduced the principle of original horizontality and principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment .
Simplified: The subject was established by Nicolaus Steno whose book De solido contained the law of superposition , the principle of original horizontality and the principle of lateral continuity in layers of sediment .