For many years two causes prevented the building of vessels of such large dimensions as those just described for lake navigation. One of these was the insufficient size of the lock at Sault Ste. Marie, and the other was the shallowness of the water on the St. Clair flats and at other points. The former difficulty disappeared in 1881 when the first of the large locks was opened at the Sault; the second difficulty was overcome by the Northern Steamship Company in the peculiar construction of their vessels with a water ballasting system that permits of sinking the ship to the depth required for navigating the deep waters of the lakes and of floating them over the shoals and bars that obstruct the navigation. This ingenious device, however, can only be regarded as a temporary expedient, pending the action of the United States Government, which contemplates the making of a twenty-one foot channel at all points where the shallows occur. This is a measure felt to be due to the lakes’ marine, which has already done so much to develop the resources of the North-West, especially the mineral resources, which would otherwise have lain comparatively dormant. “The United States have expended some $12,000,000 in widening and deepening channels, which has already been more than repaid by the rapid development of commerce. The largest item in the lakes’ traffic is the transportation of iron—the richest ores are now being mined along a line of coast of one thousand miles, dotted with manufacturing towns.”[51] It helps one to realize the immensity of the lakes’ traffic to learn that the number of vessels that cleared from the district of Chicago in 1893 was 8,789, with a gross tonnage of 5,449,470 tons—actually a larger tonnage than cleared from the port of Liverpool in 1892.[52] The tonnage passing down the Detroit River from lakes Superior, Michigan and Huron, during the seven or eight months of navigation, is, by official statements, greater than the entire foreign and coastwise trade of London and Liverpool combined in twelve months. It is estimated by competent experts to be three times greater than the foreign trade of the port of New York, and to exceed the aggregate foreign trade of all the seaports of the United States by 10,000,000 tons! SAULT STE. MARIE SHIP CANALS.