

Down had an area of 952 sq mi square miles (2,466 sq square km), and it had three areas of high ground. In the south , are the Mourne Mountains (Slieve Donard, 2,796 ft [852 m789 feet [850 metres]) are , composed of Eocene (38,000,000-year-old) granite; and in the centre are the Caledonian granite mountains of Ballynahinch (Slieve Croob, 1,755 ftfeet). The land falls westward to the Newry Basin and the River Bann and eastward to the Ards Peninsula, enclosing Strangford Lough (inlet of the sea), a large tidal inlet. A belt of glacially deposited ovoid hills (drumlins) extend westward from former central County Down. The basic geology is Silurian, with much slate and sandstone. The climate is temperate, rainfall varying from 65 in. inches (1,650 mm) a year in the Mournes to less than 35 inches in . in the east and north. Although soils of the southern slopes in the north are very fertile, a shallow stony loam predominates.
