Rock units are named for the area they were first describe in and mapped as formations and groups of formations based on the fossil content or by absolute dating methods. These rock units can be identified in widely separated places around the world, correlating the age and fossil contents. Any one geologic map will only list the time periods found in the area covered by the map, not all possible units in the world. The Geologic Time Scale is shown to the right. The classifications, associated ages, and occurrences of flora and fauna are shown.
Geologic maps are difficult to read for some who have never seen one.
45 Geologic Time Scale . Return to the index of student's work .