AbstractA thick succession of Middle Caradoc sediments (Glanrafon Beds) with occasional volcanic horizons is described. Faunas found within the succession prove a Soudleyan to Lower Longvillian age for these sediments. Detailed mapping has shown the presence of an unconformity between the Glanrafon Beds and the overlying Lower Rhyolite Tuff of the Snowdon Volcanic Series. A new fauna from the sediments within the Capel Curig Volcanic Series proves a Soudleyan (?Lower) age for this period of vulcanicity.