Final answer:
The statement that sediments are initially deposited horizontally is true, aligning with the principle of original horizontality and the law of superposition.
Step-by-step explanation:
The statement that sediments are initially deposited horizontally is true. This concept is part of the principle of original horizontality, which is closely related to the law of superposition. The law of superposition, formulated by Nicolas Steno, posits that in a sequence of undisturbed sedimentary layers, the oldest layers are on the bottom with the younger layers on top.
According to this principle, any tilting or folding must have occurred after the deposition of the sediments. Walther's Law further explains how the vertical succession of sedimentary rock facies reflects lateral changes in the environment of deposition.