The rocks underlying the National Park are typical of the Twelve Bens area and are termed metamorphic rocks. These rocks derive from sediments deposited in a warm shelf sea between 700 and 550 million years ago. Upheavals in the earth's crust formed the sediments into crystalline schists within the roots of an elongated mountain belt. Regional uplift and erosion have since brought the rocks to the surface. The mountain tops are mostly of more resistant quartzite, while the flanks consist of less resistant schists and grey marbles. The last Ice - Age, which ended about 10,000 years ago, imposed a final shaping to the landscape and left behind localised deposits of sand and gravel, widespread boulder clay and erratic boulders. These features largely determine the pattern of plant communities in the Park.