The line of navigation by the St. Lawrence did not extend beyond Lake Ontario until the Welland Canal was constructed. This important work is thirty-two miles long, and admits ships of one hundred and twenty-five guns, which is about the average tonnage of the trading-vessels on the lakes. The Niagara Strait is nearly parallel to the Welland Canal, and more than one third of it is not navigable. The canal, by opening this communication between Lake Ontario and Lake Erie, has conferred an immense benefit on all the districts west of Ontario. The great Erie Canal has been still more beneficial, by connecting the lakes with New York and the Atlantic by the Hudson River, which the canal joins after a course of three hundred and sixty miles. The effect of these two canals was quickly perceptible in the increased activity of commerce on Lake Erie, and the Erie Canal has rendered this lake the great line of transit from New York to the Western States. Lake Erie is the most shallow of all the lakes, its average depth being only sixty or seventy feet. Owing to this shallowness the lake is readily disturbed by the wind; and for this reason, and for its paucity of good harbors, it has the reputation of being the most dangerous to navigate of any of the Great Lakes. Neither are its shores as picturesquely beautiful as those of Ontario, Huron, and Superior. Still it is a lovely and romantic body of water, and its historic memories are interesting and important. In this last respect all the Great Lakes are remarkable. Some of the most picturesque and interesting chapters of our colonial and military history have for their scenes the shores and the waters of these vast inland seas. A host of great names--Champlain, Frontenac, La Salle, Marquette, Perry, Tecumseh, and Harrison--has wreathed the lakes with glory. The scene of the stirring events in which Pontiac was the conspicuous figure is now marked on the map by such names as Detroit, Sandusky, Green Bay, and Mackinaw. The thunder of the battles of Lundy's Lane and the Thames was heard not far off, and the very waters of Lake Erie were once canopied with the sulphur smoke from the cannon of Perry's conquering fleet.