But the time had to come when this wilderness would be approached on all sides, attacked, penetrated to the heart. Such wealth of resources could not be let alone or remain unused. As respects the development of the region, the industrial problem may be said to have taken two forms--the one, the development of the coal and iron on opposite sides of the mountains, the manufacture of coke and iron and steel, the establishment of wood-working industries, and the delivery of all products to the markets of the land; second, the bringing together of the coals on the north side and the ores throughout the south. In this way, then, the Cumberland Mountain no longer offered a barrier merely to the civilization of Kentucky, but to the solution of the greatest economic problem of the age--the cheapest manufacture of iron and steel. But before the pressure of this need the mountain had to give way and surrender its treasures. At any cost of money and labor, the time had to come when it would pay to bring these coals and ores together. But how was this to be done? The answer was simple: it must be done by means of natural water gaps and by tunnels through the mountain. It is the object of this paper to call attention to the way in which the new civilization of the South is expected to work at four mountain passes, and to point out some of the results which are to follow. II On the Kentucky side of the mighty wall of the Cumberland Mountain, and nearly parallel with it, is the sharp single wall of Pine Mountain, the westernmost ridge of the Alleghany system. For about a hundred miles these two gnarled and ancient monsters lie crouched side by side, guarding between them their hidden stronghold of treasure--an immense valley of timbers and irons and coals. Near the middle point of this inner wall there occurs a geological fault. The mountain falls apart as though cut in twain by some heavy downward stroke, showing on the faces of the fissure precipitous sides wooded to the crests. There is thus formed the celebrated and magnificent pass through which the Cumberland River--one of the most beautiful in the land--slips silently out of its mountain valley, and passes on to the hills and the plateaus of Kentucky. In the gap there is a space for the bed of this river, and on each side of the river space for a roadway and nothing more. [Illustration: CUMBERLAND GAP.]