In Central Park, Manhattan schist and Hartland schist, which are both metamorphosed sedimentary rock, are exposed in various outcroppings. The other two types, Fordham gneiss (an older deeper layer) and Inwood marble (metamorphosed limestone which overlays the gneiss), do not surface in the park.[1][2][3] Fordham gneiss, which consists of metamorphosed igneous rocks, was formed a billion years ago, during the Grenville orogeny that occurred during the creation of an ancient super-continent. Manhattan schist and Hartland schist were formed in the Iapetus Ocean during the Taconic orogeny in the Paleozoic era, about 450 million years ago, when the tectonic plates began to merge to form the supercontinent Pangaea.[4] Cameron's Line, a fault zone that traverses Central Park on an east–west axis, divides the outcroppings of Hartland schist to the south and Manhattan schist to the north.[5]