But the eccentricity itself of the earth in its orbit between perihelion and aphelion varies, and since the eccentricity is now at its minimum, three million miles, we infer that our last glacial epoch occurred ten thousand five hundred years ago, and the ice mantle has retreated from 39° in New Jersey to 61° in Southern Greenland, which is now covered by a glacier twelve hundred miles long, four hundred miles wide, and a mile thick, while the ice in the Southern Hemisphere has increased to several miles in thickness, and to such extent, that the nearest point to the South Pole Sir Ross was able to reach, was still fourteen hundred miles from the Pole. While the St. Lawrence and the area of the Great Lakes were under these glaciers, of course there could have been no outlet to the Atlantic of the waters, which were forced by the Alleghenies to flow to the Gulf, at the time of the great thaw ten thousand years ago, and the St. Lawrence could only have been formed after the ice had retreated beyond the Great Lake areas. Since that period the Niagara has been cutting its way from Lake Ontario through the solid limestone of the Upper Silurian Period, until the Falls of Niagara are now seven miles from the lake. Dana estimates that the river has cut its way at the rate of a foot a year, which would make it thirty-five thousand years cutting its channel. Sir Charles Lyell, as quoted in Hugh Miller’s “Testimony of the Rocks,” estimates the rate at fifty yards in forty years, which would make it ten thousand years, which agrees exactly with the time the glacier crossed the Great Lakes. However long it was, man was here then, for a tooth of a man has been found with that of a mammoth in the Drift of the Niagara, and Dr. Abbott has found bones of the mastodon and the wisdom tooth of a man, fourteen feet under the gravel of the Delaware, and their rolled and abraded surfaces prove them either pre-glacial or contemporaneous with glaciers. While the great glaciers were breaking up at the head-waters of the Platte, Yellowstone and Missouri, the flooded rivers dropped their sediment in the vast inundated lakes, whose rich bottoms formed the loess which so well characterizes the fertile prairie soil of the Western States to-day. In Nebraska, stone arrow-heads and the bones of the ancient elephant were found thirty feet under the loess, and in Greene County, Illinois, a well was dug seventy-two feet through the loess, when a stone hatchet was found, proving that the hatchet was dropped there when Illinois was covered by a lake over which the rude hunter paddled his canoe. Dr. Koch, of St. Louis, found the bones of the mastodon in the Osage Valley in Missouri, which was killed while mired down, by fire being built around it, which consumed nearly all the bones of the animal except the legs and toes. The presence of ashes and stones proves conclusively that the huge animal met his death at the hands of man.