What principle did the studies of James Hutton and Charles Lyell contribute to? Horizontality, which states that if sedimentary rocks are not found in horizontal
layers, they have been rearranged by the forces within Earth.
Superposition, or the fact that older rock layers are found below newer rock
layers in undisturbed sedimentary rock.
Uniformitarianism, or the fact that geological processes have always operated in
a similar way for the entire history of Earth.
Unconformities, which states that folding, tilting, erosion, or other breaks in the
rock record can provide clues to Earth's past.