Some aspects of the growth of manufacturing in the North are well illustrated in the development of the mineral resources around Lake Superior. The presence of copper and iron in this region had long been known, but they had not been utilized until a decade before the Civil War, and even then the output had been greatly restricted by insufficient transportation facilities. By the close of the war, however, a canal had been constructed which allowed the passage of barges from Lake Superior to Lake Huron, and railroads had been laid to a few important mining centers. The Marquette iron range in northern Michigan, the Gogebic in Wisconsin and Michigan, the Menominee near Marquette, the Vermilion Lake and Mesabec ore-beds near Duluth,--all these combined to yield millions of tons of ore, caused the development of numerous mining towns and laid the foundations of a gigantic expansion in the production of steel. As the iron and steel industry with its furnaces, machinery and skilled labor was already established at points in Illinois, Ohio and western Pennsylvania, it was cheaper to transport the ore to these places than to transfer the industry to the mines. Ore vessels were constructed capable of carrying mammoth cargoes; docks, railroads and canals were built; and the products of the mines taken to lake and inland cities. Improvements, meanwhile, were being continually made in the steel industry, such as the Bessemer process, by which the impurities were burned out of the iron ore, and exactly enough carbon introduced into the molten metal to transform it into steel. Although the steel industry was established in many places, its most dramatic growth occurred in those parts of eastern Ohio and western Pennsylvania that center about the city of Pittsburg. Placed strategically at the point where the Allegheny and Monongahela rivers join to form the Ohio, in the midst of an area rich in coal, petroleum and natural gas, Pittsburg rapidly became the center of a region in which the development of manufacturing and the construction of railroads dwarfed other interests. A large portion of the ore mined in the Lake Superior fields was carried to the Pittsburg district to be transformed into steel products of all kinds. Moreover, the fortunes made by private individuals in the region, and the inflow of alien laborers to work in the factories and on the railroads raised weighty social and industrial problems.