The Early Pleistocene is represented on the West Coast of the South Island by theOld Man Group, which between the Grey Valley in the north and Ross in the south is composed of three formations. TheDonnelly Conglomerate(up to 400 ft) (oldest) composed mainly of tectonic gravels, with finer beds and lignite at the base and thin valley or piedmont glaciation deposits at the top. TheJones Formation(up to ?400 ft) consists of till and glacial siltstone with minor sandstone and lignite. There may have been two ice advances, but there is no evidence of an interglacial period. TheHumphreys Conglomerate(up to 5,000 ft) (youngest) consists of tectonic gravels. Contemporaneous movements occurring when the Kaikoura Orogeny approached its climax, folded all these deposits. Late weathering has decomposed many of the components of the conglomerates.