Facing each other across across the Eden valley, the gentle rounded outlines of the north Pennines contrast starkly with the frowning cliffs and steep-sided valleys of the Lakeland hills to the west. Whilst Lakeland hills are a confused jumble of metamorphic and igneous rocks, deeply scored by glacial action, the north Pennines are an essentially simple structure of deep beds of Carboniferous marine sediment, perched upon a rigid raft of granite, the whole forming the 'Alston Block'.