The oldest of these are the limestones and associated mudstones which outcrop in the northernmost part of the region, though which are thought to underlie the entire area at depth. These are assigned to the Craven Group.
The oldest geological formations in this area comprise the limestones and mudstones that are visible on the surface in the northernmost part of the region, although it is believed that these underlie the entire area at a deeper level. They are designated as part of the Craven Group.