Another effect of the glacial period has been the creation of numerous waterfalls throughout the glaciated area. The most notable instance is that of the Falls of Niagara.
In preglacial times the beds of all rivers and water courses had worn down to an even slope, so that there were very few, if any, waterfalls such as we have to-day. As we have before stated, Niagara River as well as the St. Lawrence River is a new outlet for the drainage of the great lakes. A part of this drainage formerly had its outlet through the Mohawk Valley into the Hudson, which is now filled up with glacial drift. The evidence is so conclusive that it is no longer doubted that the Niagara River dates from the time that the ice receded from that point. When the water first began to flow through this new channel it plunged over the high rocky cliff at Queenstown, and from that time to this it has been wearing its way back to the present position of Niagara Falls, a distance of about seven miles. A vast amount of interest centers about this river because it is the best evidence we have of the time that has expired since the glacial period. A great deal of study has been given to determine the amount of erosion at the Falls during a year's time. If this could be accurately determined, then by measuring the distance from the present falls to Queenstown, we could easily determine the number of years since the ice period. It is difficult to determine, for the conditions may have changed; for instance, the rock at the Falls to-day is said to be harder than it is further down toward Queenstown. The estimates vary from 35,000 years to 10,000 years--that is, from a rate of erosion of five feet to one foot, per year.
Every science is, nearly or remotely, related to every other science. If we could determine accurately the date of the ice period it would settle a whole lot of other questions that are related to it, and one of them is the antiquity of man. Many stone implements such as were made and used by the aborigines have been found at various times buried deeply under the glacial drift. These finds have occurred so often that there no longer remains a doubt but that a race of men existed on this continent in preglacial times. There are evidences that at a time long ago the temperate zone extended far north of this, and it is not impossible that what is now the continent of Asia and that of North America were joined. In fact, they come very close together to-day at Bering Strait. If such were the case this continent could have been inhabited from the old world by an overland route. This, however, is mere speculation. There are a number of factors that are taken into account in determining the period of the ice age besides the Niagara River and the Falls. The Falls of St. Anthony at Minneapolis (which like the Niagara is a creature of the ice age), the wear of water on the shores of the great lakes, the newness of the rocks that are piled up on the terminal moraines, all point to a much shorter period since the ice age than it used to be supposed, and indicate that the time does not exceed 10,000 years.