The geology of Kimmeridge civil parish comprises bedrock formed in the Late Jurassic epoch, overlain in many places by superficial Quaternary head deposits. The bedrock is mostly Kimmeridge clay, except for the top of Smedmore Hill and along to Swyre Head, which is formed from Portland stone. Between this and the Kimmeridge clay, and outcropping just beneath the top of the hill, is a thin band of Portland sand. Landslip deposits from the Portland stone cover most of the steep southwest-facing slopes of the hills. Within the Kimmeridge clay are bands of bituminous shale and dolomite, which form flat ledges within Kimmeridge Bay that are exposed at low tide.