A fossil should be labeled with as much information as possible, including the species or genus if known, the collecting location, rock unit, collector, and date collected. The rock unit normally refers to a formation, a sequence of rocks layers sharing certain features and usually deposited under similar conditions. Examples of formations are the Cleveland Shale and the Glen Rose Limestone.
Geologists often subdivide formations into smaller units called members or beds.
When the identity of a fossil is unknown, it is important to record at least the name of the formation and collecting locality. Also helpful to include on a label, especially if the item will be displayed, is the geologic period of the host formation, such as Lower Cretaceous or Upper Jurassic. Information about geologic formations in an area and their geologic ages is found in publications and maps by the U.S. Geologic Survey and other academic works, including fossil collecting guidebooks. When collecting with a group, normally you will be given the name of the formation and its geologic age. Rather than try to write all pertinent information on the fossil itself, most collectors and curators use labels or index cards, which are then affixed to the specimen, placed in the same container, or recorded in a notebook.