DURING the Devonian period (419-359 million years ago), desert conditions prevailed with the deposition of Old Red Sandstone (ORS) sediments.

In Cumbria the ORS has been removed by erosion associated with a major and complex period of mountain-building that lasted 50 million years. The Acadian Orogeny occurred when two continents collided through the process of continental drift.

Ordovician and Silurian rocks were deeply buried, folded and uplifted to form mountains in the Lake District. Intense pressure and heat altered the rocks creating the distinctive slates.

This created complex structures making recognition of many Lakeland rocks more difficult. Magma, formed by crustal melting, was intruded into the crust forming granite at Skiddaw and Shap and other minor intrusions.