How are the basic units of Geological formations established?
In their study of earth history, geologists have developed conventions for naming and identifying rock units. A formation is defined by layers of rock that are everywhere the same age and have physical characteristics and properties that are somewhat consistent. Formations are named for a geographic location that best typifies the characteristics of the rocks that are part of that layer. The Morrison Formation is named for a location near the town of Morrison,Colorado. The rock here is a crumbly, fine grained, fine layered shale. It has been studied extensively by geologists for over 100 years because of the spectacular dinosaur skeletons that have been excavated from this formation. However, this rock unit is found across the Western United States and is identified by comparing what is seen at the type locality in Morrison, Colorado.
