and so continued until the limestone again appeared in its natural position.
There are no rock-bluffs below the confluence of the Ohio with the Mississippi, but about thirty miles above that point they abruptly rise on both sides of the river at what is called the Grand Chain, a high rock ridge traversing the region from east to west, and which lies at a considerable height above the sea-level. There, in all probability, the river had its original outlet, and there, without doubt, the cataract process began, although the character of the stratification is unknown to us. At the time the erosion was in progress, there must have been several times the present volume of water flowing in the river, spreading out wider than the bluff, even, as an occasional terrace shows. The same perpendicular rock-walls and sand-bottom characterize the Wisconsin River for a distance of eighty miles from its junction with the Mississippi; the position and character of the stratification being much the same, indicating that the same agency was active in the erosion of both channels.
St. Anthony Falls have been studied by Professor Winchell, and he has arrived at the conclusion from various data that the falls have worked their way back from a point near Fort Snelling to where they now are, a distance of about eight miles, since the glacial period, and he estimates that it has taken about five thousand years to accomplish the work, which estimate, taken as a basis of calculation, and allowing a margin of at least one third, gives us the time necessary to cut out the entire channel at, say, four hundred thousand years; and this, if, as we maintain, the cataract process wrought the gorge not only from Fort Snelling northward, but from far down the river, at or near the ancient outlet, is without doubt a conservative estimate of the time actually required.
We have thus briefly outlined the new theory of the Mississippi erosion, and this is written with the expectation that the barbed arrows of scientific criticism will be aimed toward it; but, if so, it will aid in the solution of a question hitherto little studied. Many things point toward the theory here advanced as being at least quite possible, and even probable. Its final solution will, however, necessitate painstaking investigation, with the attention directed to that especial object.
