Ordovician

Westmorland Slate

January 1, 201312:00 pmMay 3, 2017 2:48 pm

Also known as Honnister Slate, this is variety of slate from the Borrowdale Volcanic Group of Cumbria. Unusually it is formed from a tuff (volcanic ash deposit) – erupted during the Caradoc Age of the Ordovician (458 to 448 million years ago) – which has been subjected to high pressure and heat, metamorphosing it to […]