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Niagara Falls at the American Association.—Professor Pohlman presented his theory of the origin of the Niagara gorge to the American Association at its recent meeting. This theory differs essentially from the views usually accepted by geologists, that Niagara Falls were originally at Lewiston, and the river has since excavated the chasm through which it flows, thence to the present position of the falls. Professor Pohlman's view is based on a careful survey of the district appertaining to the Niagara basin, which he distinctly defines, with its ancient river-beds, and of the ancient beach-marks on the lake-shores that testify to the gradual subsidence of the water. It supposes that the ancient Tonawanda River flowed into the valley of the present Niagara at about the same place as where it enters now; that the original point of overflow of its waters across the thin-bedded Niagara limestone was perhaps somewhere near or a little southerly from the upper rapids at the present falls; that from here the waters met no obstacle, and in their flow predetermined the river-gorge between the falls and the Whirlpool, and continued in a straight course north through the valley of St. Davis. They descended over the escarpment at the latter place, and along this line in the course of time the three falls over the Medina sandstone and the Clinton and Niagara limestones were formed. During the glacial period the natural drainage-lines were closed up, and a great lake was formed. After the disappearance of the ice-sheet, when the water had subsided to about 605 feet above the ocean, or stood on a level with Lewiston Heights, Lake Erie and Lake Ontario formed two large bodies of water, separated by a mud-flat which extended from Buffalo to Lewiston. Then, as Professor Pohlman attempts to show from the terraces, the two lakes drained simultaneously, and were connected by a river with a more or less swift current, but without any fall, simply deepening its bed in the drift and shaping its course along the buried pre-glacial valleys. But, when the waters reached the Niagara lime-stone at the edge of the Lewiston escarp-
