The southwestern corner of the State contains excellent beds of clay, deposited by the seas and now used for building materials and pottery. Two beds in the Dickinson vicinity, each containing approximately 29 million cubic yards, yield the finest clays in the State. A layer of yellow sand clay overlies the whitish plastic variety here; the two combine to form a number of colors, and have the added advantage of being free from iron. Plastic clay beds of importance, although not so valuable commercially as the Dickinson deposits, are found throughout the southwestern corner of the State. They yield one of the rarest and most valuable types of clay for pottery and other specialized purposes. Shales found near the western clay beds are used in the manufacture of cheaper building materials. The discovery of two large bentonite fields in southwestern North Dakota in 1930 opened up a new mineral resource. This claylike mineral is used as a binding agent and filler in many commercial processes, such as the manufacture of soaps, paints, and cosmetics. The larger deposit--in the Little Badlands--covers 25 square miles and contains about 100 million tons of the mineral, while the Chalky Butte deposit near Amidon contains about 60 million tons. The beds are easily accessible, being uncovered in many places. Extensive sodium sulphate deposits have been formed in old lake beds in the northwestern corner of the State, where the mineral-bearing waters have evaporated, leaving a deposit of sodium sulphate crystals. North of the town of Grenora, 1,150 acres are covered with sodium sulphate beds ranging from a few inches to more than 30 feet in depth. Miller, North, and McKone Lakes, near Alkabo, contain more than 20 million tons. Sodium sulphate, also known as Glauber's salt, is commercially valuable, especially in the pulp and paper industries. Owing to lack of knowledge of its existence in this country, it has been imported largely from Canada. Although geologists have doubted that oil exists in commercial quantities in North Dakota, considerable interest has been shown in the wells near Marmarth in the southwestern corner of the State. Their proximity to the Montana oil fields increases the possibility of the success of these wells. Much interest has also been shown in the development of a potential oil field south of Ray in northwestern North Dakota.