In all its features and characteristics the great water-course, including the great lakes, which feeds the Niagara, is peculiar and interesting. It is more than two thousand miles long; its utmost surface-sources are scarcely six hundred feet above tide-water; its bottom, at its greater depth, is more than four hundred feet below tide-water. In all its course it receives less than two score of affluents, and only two of these, the St. Maurice and the Saugeen, bring to it any considerable quantity of water, and no flood in any of them discolors its emerald surface from shore to shore. Only fierce gales of wind bring up from its own depths the sediment that can discolor its whole face. Far the greater portion of its water-supply is drawn from countless hidden springs, lying deep in the bosom of the earth. In all the elements of beautiful, picturesque, and enchanting scenery it is unrivaled. The rapids of the Niagara just above the Falls, from the Leaping Rock down through the Witches' Caldron to the edge of the precipice, are nearly a mile in width, and discharge ten million cubic feet of water each minute. But for a combination of grandeur and beauty, and for imparting a sense of almost infinite power, nothing can surpass the Whirlpool Rapids below the Falls, where the ten million cubic feet of water are compressed into a tortuous, tumultuous channel, less than four hundred feet wide. There are many lesser rapids in the St. Lawrence, from the Thousand Islands to Montreal, the passage of which in the large lake steamers is an exciting voyage. The constant changes of scenery at every turn and in every rood of progress is almost bewildering. Then the alternation of rapids and broad expanses of river, the bird-like motion as the steamer sinks and sails down through the rapids, and the sense of relief when it seems to rise and glide over the smooth river, vary and increase the excitement. There is developed in one of those expanses a peculiar geological feature called the Split Rock. The name is strictly accurate. The descending steamer finds but one narrow channel, a little more than its own width, through which it can pass in a stream more than half a mile wide. It lies between the sharp corners of a broad, wedge-shaped cleavage in an immense rock which, by some convulsion of nature--not by any abrading process of the elements--has been literally split downward more than eighty feet. The last crooked and turbulent rapid passed just before reaching Montreal is the terror of the river pilots, and they never attempt its passage except by daylight. From Montreal to the Gulf of St. Lawrence the constantly deepening channel flows with an unbroken current.