A little more than thirty years ago, Professor Agassiz made a tour to the Upper Lakes with a class of students, for the purpose of giving them practical lessons in geology and other branches of natural science. The day was devoted to outdoor examinations of different localities, and in the evening was given a familiar lecture expository of the day's work. One of the places thus visited was Niagara, and it was the writer's good-fortune to be able to listen to the instructive lecture which followed the examination. Professor Agassiz concurs with other geologists in the opinion that the Falls were once at Lewiston, and one of the most interesting portions of the lecture was his animated description of the retrocession of the Falls, traced step by step back to their present position. From this oral exposition, from other high geological authorities, and from personal observation extending through a quarter of a century, the writer has derived the facts herein presented.
There can be no doubt that at a comparatively recent geological period the Falls of Niagara had no existence. It may suffice to mention two facts which are conclusive on this point. Dr. Houghton, geologist of the State of Michigan, stated in his report that the elevation of Lake Michigan above tide-water is five hundred and seventy-eight feet. That of Lake Erie, as shown by the surveys of the Erie Canal, is five hundred and sixty-eight feet, the difference of level between the two being ten feet. The fall or descent in the Niagara River from Lake Erie to Gill Creek, a few rods above the site of old Fort Schlosser, is twenty feet. Hence we learn that the surface of the water in Lake Michigan is thirty feet higher than that of the Niagara River near the mouth of Gill Creek. If, therefore, we find anywhere below the Falls a barrier drawn across this river that is more than thirty feet high, its water would thereby be set back to Lake Michigan. A moderate elevation above this thirty feet would serve as a safe shore-line for still water.
The existence of this barrier has been demonstrated. In the year 1835, by direction of the War Department, Captain W. G. Williams, of the United States Topographical Engineers, surveyed three routes for a canal around Niagara Falls. The first of these routes was run from the river nearly in a straight line to the head of Bloody Run, and thence a portion of the way over the terrace laid bare by the rapid subsidence of the water after the barrier had been broken through. The second route, commencing at the same point with the first,--the old Schlosser Storehouse, just above Gill Creek,--was run up the valley of the creek, through the ridge above Lewiston, at a slight depression in the general line of the hill, and thence to Lake Ontario by two different routes. The highest point in the ridge was found to be sixty feet above the surface of the water in the river at the starting point. Here, then, is found the requisite barrier--a dam thirty feet higher than the water in Lake Michigan, and having a base, as will be seen by reference to the map, of two and a half miles in breadth. This was its breadth at the time of the survey. But a careful observance of the topography of the banks on both sides of the river will show that it must have been originally not less than twice that breadth, and that the depressions now existing are the results of the denudation caused by the removal of the barrier.