The four columns in this diagram represent fossil-bearing sedimentary rock layers at four different sites. The sedimentary layers are continuous except at the zigzag lines, which represent unconformities. Compare the sites to determine the relative ages of the fossils from The four columns in this diagram represent fossil-bearing sedimentary rock layers at four different sites. The sedimentary layers are continuous except at the zigzag lines, which represent unconformities. Compare the sites to determine the relative ages of the fossils from youngest to oldest..