These rocks were then uplifted to become mountains.Based on those assumptions, Steno made a remarkable series of conjectures that are now known as Steno's Laws.Crosscutting Relations are those where one rock literally cuts across another, such as for example when igneous dikes and sills are emplaced in fractures within a pile of sedimentary rocks (see picture at left).
The principle states that in a sequence of undeformed sedimentary rocks the oldest beds are at the bottom and the youngest ones are at the top.
Instead of invoking supernatural forces to explain fossils, Steno concluded that fossils were once parts of living creatures.
He then sought to explain how fossil seashells could be found in rocks far from any ocean.
Because sediments are deposited under water, they will form flat, horizontal layers (Figure 11.11).
If a sedimentary rock is found tilted, the layer was tilted after it was formed.