Geology Group visit to Treak Cliff Cavern, Castleton. November 2018. On 20th November  the Geology group made their last visit of 2018 to the Treak Cliff Cavern in the Hope Valley at Castleton to experience the wonderful phenomena of ‘Blue John’. It is a very rare variety of the mineral Calcium Fluoride, also called Derbyshire … Continue reading Geology Archive 2018