That is, with increasing age, the amount of rock of that age decreases. This is supported by the fact that the Earth is a dynamic planet and that the processes introduced in the section on Plate Tectonics have resulted in a recycling of crustal rocks. The history of the Earth is broken up into a hierarchical set of divisions for describing geologic time. As increasingly smaller units of time, the generally accepted divisions are Eon, Era, Period, Epoch, and Age. In the time scale shown below, two levels of this hierarchy are represented.
Geologic maps show the pattern of rocks on the surface of the earth.
Geologic sections show the patterns of rocks as they might be exposed on the side of a road cut or on the wall of a trench. One of the things that geologic sections show very well is the geological history of an area. The fossiliferous deposits belong to the Chesapeake Group of Miocene age geological strata in the Atlantic Coastal Plain region. These deposits are exposed in cliffs up to 100 feet high between Chesapeake Beach and Drum Point and constitute the most complete section of Miocene deposits in the eastern United States.