Oldal 80 [80]
OCR
GEOLOGICAL. . There are few who see the Niagara gorge but that wonder what the facts are in regard to its formation. Geologists tell us, and their answer is accepted as conclusive, that it started at the mountain near Lewiston. The whole waters of the lakes there foamed over this dam, which was several miles in width. This accounts for the shells, etc., which have been found on Goat Island, it having been submerged ; also for the shells found on the land along the river up stream, shells which enabled Lyell, Hall and others to prove that the Niagara once flowed through a shallow valley. That it cut the gorge is geologically equally decided. There is no better place to study geology and the strata of rocks than this gorge that Niagara has cut. It is said that not only has Niagara cut the gorge ; it has carried away the chips of its own workshop. The slate being probably crumed, is easily carried away. But at the base of the fall we find large boulders, which by some meaus or other, are gradually removed down the river, The ice which fills the gorge in winter and which grapples with the boulders has been © regarded as the transporting agent. Probably it is to some extent. But erosion acts without ceasing on the outbutting points of the boulder, thus withdrawing their support and urging them down the river. Solution also does its portion of the work. That solid matter is carried down is proved by the difference of depth between the Niagara and Lake Ontario, where the river enters. The depth falls from seventy-two to twenty feet in consequence of the solid matter caused by the diminished motion of the river. Near the mouth of the gorge at Queenston, the depth, according to the Canadian Admiralty Chart, is 180 feet, while within the gorge it is 132 feet. Prof. James Hall, in his geology of the 4th district of New York State, suggests the possibility of there having been three separate falls, one above the other, when the falls first began to recede. The face of the gorge from the falls at Lewiston and along the ridge shows us exactly through what kind of rocks the gorge was cut. Professor Hall gives these as the strata ot the rocks : iB Niagara limestone ; 2, soft shale ; 3, compact grey limestone ; 4, shale; 5, sand-stone constituting, with Nos. 6, 7 and 5, the Medina group ; 6, shale and marl : 7 guartz sandstone ; 8, red sandstone. Further facts and ideas are found in the writings of Prof. G. K. Gilbert, of the U. 5. xeological Survey. He say that ‘‘ one might suspect. "after a hasty examination, the two sides had been left asunder by some Plutonic agency. But those who have -made a study of the subject have reached the conclusion that the trench was excavated by running water, so that the strata of the two sides are alike because they are parts of continuous sheets, from each of which a narrow strip has here been cut. The contour of the cataract is subject to change. From time to time blocks of rock break away, falling into the pool below, and new shapes are then given .
