Situated just south of Dublin, County Wicklow is dominated by a great mass of domed granite mountains, penetrated by deep glens and wooded valleys. The most beautiful parts of Wicklow can be found within a broad north-south swade running down the centre of the mountains. The county's rolling granite hills are also the source of Dublin's River Liffey. Located among these hills and mountains are places such as Glencree, Glenmalure, Glenmacnass and the magnificent Glen of Imaal. Wicklow's mountains were molded and shaped during the Ice Age, resulting in the smooth peaks that we see today. It was this ice that was responsible for creating the deep valleys of Glenmacnass, Glenmalure and Glendalough. A vast mound of granite, the mountains are comprised of a hot igneous rock that consolidated some 400 million years ago. Baking the overlying clays and sedimentary rock, the heat produced shiny mica shists, evident across the county.