Which of the following is a correct principle of relative-age dating?

a. in undisturbed rock layers, the youngest rocks are on the bottom.
b. rock-forming materials are deposited in horizontal layers, though they may be tilted later.
c. sediments are deposited in lateral sheets, but their orders often change.
d. if one rock contains pieces of another, the rock containing the pieces is older than the pieces.

The correct answer is B) Rock-forming materials are deposited in horizontal layers, though they may be tilted later.  

The option that is a correct principle of relative-age dating is "Rock-forming materials are deposited in horizontal layers, though they may be tilted later."

When using relative dating, scientists consider six principles to determine the relative age of the formation. These are the Principle of Superposition, the Principle of Original Horizontality, the Principle of Lateral Continuity, the Principle of Cross Continuity, the Principle of Inclusions, and the Principle of Fossil Succession.