In reply to Siward: The Borrowdale volcanics are circa 450m years old, which is obviously pretty darn old... and I tihnk most stuff in the lakes is of a similar generation . The Lewisian is rather older, and is a collection of rocks dating between 1.7 and 3 billion years ago accreted together. As I recall the Lewisian are rather 'deep' rocks, exposed by a long, long time to erode the overburden. The Skiddaw group and Borrowdale volcanics are deformed near surface rocks.