The St. Lawrence is an enormous river, having much the largest estuary of any river on the globe, the tidal current flowing five hundred miles up the stream, and its mouth spreading ninety-six miles wide. It is the outlet of the greatest body of fresh water in existence, draining seven vast lakes--Nepigon, Superior, Michigan, Huron, Erie, Ontario and Champlain--besides myriads of smaller ones, including the Central New York lakes, hundreds in the Adirondack forests, and thousands in the vast Canadian wilderness. The St. Lawrence basin covers a territory of over four hundred thousand square miles, and has been computed as containing more than half the fresh water on the planet. The main St. Lawrence river is seven hundred and fifty miles long from Lake Ontario to the head of the Gulf, while the total length of the whole system of lakes and rivers is over two thousand miles, and has been computed by some patient mathematician to contain a mass of fresh water equal to twelve thousand cubic miles, of which one cubic mile goes over Niagara Falls every week. The early geographers usually located the head of the system in Lake Nepigon, north of Superior, but it is thought the longer line to the ocean is from the source of St. Louis River, flowing through Minnesota into the southwestern extremity of Lake Superior at Duluth. The bigness of the wonderful St. Lawrence is shown in everything about it. Thoreau, who was such a keen observer, has written that this great river rises near another "Father of Waters," the Mississippi, and "issues from a remarkable spring, far up in the woods, fifteen hundred miles in circumference," called Lake Superior, while "it makes such a noise in its tumbling down at one place (Niagara) as is heard all round the world." The geologists, however, who usually upturn most things, declare that it did not always reach the sea as now. Originally the St. Lawrence, they say, flowed into the ocean by going out through the Narrows in New York harbor, and its immense current broke the passage through the West Point Highlands in a mighty stream, compared with which the present Hudson River is a pigmy. Professor Newberry writes that during countless ages this enormous river, which no human eyes beheld, carried off the surplus waters of a great drainage area with a rapid current cutting down its gorge many hundred feet in depth, reaching from the Lake Superior basin to the Narrows, where it dispersed in a vast delta, debouching upon a sea then much lower in level than now, and having its shore-line about eighty miles southeast of New York. By some stupendous convulsion this channel was changed, drift banked up the old valley of the Mohawk, and the outflow was deflected from the northeast corner of Lake Ontario into the present shallow and rocky channel, filled with islands and rapids, followed by the St. Lawrence down to Montreal.