The Craven Inlier is on the southern margin of the Askrigg Block, immediately north of the North Craven Fault.  These ancient roots of the Yorkshire Dales are exposed in Crummack Dale and Upper Ribblesdale and are over 400 million years old.  These Ordovician and Silurian mudstones and sandstones began life as muddy and sandy turbidite flows into a deep ocean basin.   For almost 80 million years during the Devonian, these rocks were uplifted and folded into mountains, before weathering and erosion wore the rocks flat until they were swamped by the tropical seas of the Carboniferous period where horizontal beds of limestone, packed with fossils, formed in reef-edged lagoons around 350 to 330 million years ago.

A talk by Richard Fletcher.