This group collects the Named Rock Formations and Groups subcategory's members that are formal stratigraphic units, a rock formation, group or supergroup defined by geologists for a body of rock of a given age and origin, most of them significant as a fossil-bearing sequence: the Morrison, Hell Creek and Green River Formations of the American West, the Karoo Supergroup, the Yixian and Jiufotang Formations of China's fossil-rich Jehol Biota, and dozens of other named sandstones, shales, limestones and clays identified by their own formal stratigraphic name. This is the largest group in the subcategory, identified by each member's own name ending in a recognized stratigraphic unit term such as Formation, Group, Shale or Sandstone.