Question: If a sequence of sedimentary units is cut by a fault, what does the principle of cross-cutting relationships tell a geologist? Need Assignment Help? View Available Hint(s)for Part B All of the sedimentary units must have been deposited and lithified before being cut by the fault. Sedimentary layers are laid down horizontally. The fault is older than the sedimentary sequence. The sedimentary units on the left side of the fault are the same as those on the right side. The oldest sedimentary unit is located at the base of the sequence, while the youngest is at the top.