Iapetus closed up completely at the end of the Silurian period (443-415 million years ago) and the Wicklow Mountains were uplifted during the main phase of the Caledonian orogeny at the start of the Devonian period (415-358 million years ago) when the continents of Baltica and Laurentia collided. The collision pushed up a large batholith of granite, known as the Leinster Chain: this is the largest continuous area of granite in Ireland and Britain and runs from the coast at Dún Laoghaire in County Dublin to New Ross in County Wexford and includes the Wicklow and Blackstairs Mountains. The heat generated by the collision metamorphosed the slates and shales surrounding the granite into schists which formed an aureole (shell) around the granite. The process of erosion has removed much of the surrounding schist from the mountain tops, exposing the underlying granite. Some remnants of the schist roof remain on some of the mountain tops, most notably Lugnaquilla. The round granite-topped peaks contrast with the sharper schist peaks: for example, War Hill (granite) and Djouce (schist).