Oldal 81 [81]
OCR
to the brink over which the water leaps. Many such falls of rock have taken place since the white man occupied the banks of the river, and the breaking away of a very large section is still a recent event. By such observations we are assured that the extent of the gorge is increasing at its end, that it is growing larger, and that the cataract is the cause of the extension. This determination is the first element in the history of thesriver. A change is in progress before our eyes. The river’s history, like human history, is being enacted, and from that which occurs we can draw inferences concerning what has occured and what will occur. We can look forward to the time when the gorge now traversing the fourth part of the width of the plateau will completely divide it, so that the Niagara will drain Lake Erie tothe bottom. We can look back to the time when there was no gorge, but when the water flowed on the top of the plain to its edge, and the Falls were at Lewiston. The commencement of the cutting of the Niagara gorge is the beginning of the history of the Niagara River. We have accomplished somewhat of our purpose if we have discovered that our river had a beginning. Weare also accustomed to think of streams, and especially large streams, as permanent—as flowing on forever, so that the discovery of a definate beginning to the life of a great river like the Niagara is important and impressive. The author then considers the tendency of stream histories and the tendency of lake histories, and after citing the difference between the streams of the North and South says: At the South the whole drainage system is nature; At the North itisimmature. At the South itis old; at the North young. The explanation of this lies in a great geologic event of somewhat recent date - the event known as the age of ice. Previous to the ice age, our streams may have been as tame and orderly as those of the Southern States, and we have no evidence that they were lakes in this region. During the ice age, the region of the Great Lakes was somewhat in the condition of Greenland. It was covered by an immense sheet of ice, and the ice was in motion. In general it moved from North to South. Eventually the warm climate of the South prevailed over the invader born of a cold climate, compelling it to retreat. The ancient configuration of the country was more or less modified by the erosive action of the ice and the deposits of drift. An entirely new system of hills and valleys was given to the land. Thus it was that the whole water system of a vast region was refreshioned, and thus it has come to pass that the streams of this region are young. Like every other stream of the district of the Great Lakes, the Niagara was born during the melting of the ice." Professor Gilbert then recites the different stages of the ice period and continuing says: ‘‘ The next change in the geography of the lakes was a great one. The ice, which had pre viously occupied nearly the whole of the Ontario basin, so far withdrew as to enable accumuated water to flow out by way of the Mohawk Valley. The level of discharge was thus suddenly lowered 550 feet, and a large district previously submerged became dry land, Then for the
