Difficulties in shipping grain to outside markets provided one of the chief factors in the development of the many cooperatives which are important in the present economic life of the State. Grain farmers early realized that by acting independently they could not trade advantageously with eastern buyers. By 1891 there were ten farmers' elevators in the State, and the cooperative movement grew until the Equity Association, the National Producers Alliance, and the Better Farming Association developed the North Dakota division of the Farmers Educational and Cooperative Union of America, which at present includes some 540 buying and consumers' cooperatives in the State. At first exclusively grain-selling organizations, the cooperatives have expanded to include the handling of twine, machinery, petroleum products, tires, electricity, dairy products, and groceries. The period since the World War has seen the revival of the occupation of the first white settlers--the fur industry. Some trapping is done each winter, but the fur sellers today do not rely upon this nineteenth-century method of getting pelts. Instead they have farms on which they raise the furbearing animals, usually silver-black foxes. The climate is well suited to this industry, for the cold winters produce heavy and valuable furs. Although agriculture and its allied industries will probably always predominate, recent years have seen the beginning of the development of North Dakota's great mineral resources, which lay neglected or unrecognized for years while farmers attempted to emulate the phenomenal success of the bonanza wheat growers. Ranchers in the western counties early discovered large deposits of lignite, a black or brownish substance in a stage between peat and bituminous coal, lying at or near the surface of the earth. Lignite has a conspicuously woody appearance, often showing clearly the grain of the wood or the shape of the trunks and branches from which it was formed. It is known to underlie the entire western part of the State. For many years its use was entirely local, chiefly because it contains a large amount of moisture which evaporates upon exposure to the air, causing the coal to crumble. To overcome this difficulty, shipment is now made in closed boxcars; briquetting of lignite has also proved successful, and the mineral is now common fuel. Lignite is used exclusively by State institutions and by many of the manufacturing concerns in the State. In the eight-month period from November 1, 1935, to June 30, 1936, the production of 355 mines, amounted to 1,704,983 tons, valued at $2,077,800.15. New mines are continually being opened. The rapidity with which the industry has been developed is demonstrated by the fact that there were 67 more mines in operation in 1935 than in 1931, with production in 1935 twice that of 1924 and eight times that of 1908.