Do you think the environments indicated by me sedimentary rocks are the same in both the east and the west? Was deposition continuous (conformable) in both areas? Explain why or why not. During field mapping last year, trilobites were found in limestone units in both areas (see the figure on the next page). Paleontologists reported that these were identical index fossils from a narrow span of Middle Cambrian time. Using this additional information, draw lines indicating matching layers on the figure. Why does the presence of index fossils make correlation more accurate than correlation based on lithologic and sequence similarities alone?