The gently rolling country between the St. Lawrence River and the Adirondack Mountains is cut by the St. Regis, Raquette, Grass, and Oswegatchie Rivers, swift streams that tumble from the Adirondack slopes and flow westward and northward into the St. Lawrence. Although the French maintained an Indian mission from 1746 to 1756 at the mouth of the Oswegatchie, Ogdensburg became the first settlement in 1796. In 1791, Alexander Macomb bought four million acres in the North Country, and purchasers from Macomb surveyed the land and opened it to settlers, many of them New Englanders. The St. Lawrence Turnpike, constructed in 1810 from Malone to Carthage, improved transportation, and railroads after 1850 led to more rapid regional development. Agriculture, dairying, and maple sugar formed the basic economy, while potash production for export was an early local enterprise. Paper mills used abundant water power, which was later harnessed to supply electrical energy. Large quantities of lead, zinc, and talc are found there, near Star Lake is the world's largest open-cut magnetite iron mine, Massena is a center for aluminum production, and the St. Lawrence Seaway and the New York State Power development add much to the area's economy.