Page:Popular Science Monthly Volume 49.djvu/21

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9
NIAGARA AS A TIMEPIECE.

shown on the map of the gorge (Fig. 9), and in the longitudinal section in Fig. 16.

PSM V49 D021 Map of the niagara gorge.jpg
Fig. 9.—Map of the Niagara Gorge (United States Lake Survey), showing its Variable Width and Cross-sections.

The Whirlpool and its Ravine.—The elbow of the Niagara gorge at the whirlpool has given rise to much speculation and has led to great confusion. Fifty years ago. Sir Charles Lyell supposed that it indicated an ancient course of the river itself, which extended thence to the St. Davids' Valley, about four or five miles distant, although the country forms a level floor which told of no buried channel (see Fig. 5). This mistake arose from the perpendicular walls of the whirlpool basin, without the necessity of sloping sides for ancient valleys being then perfectly known, and without the author evidently going through the ravine where rocks were exposed. The serious feature of the mistake was that it led to the supposition that perhaps much of the gorge above the whirlpool was older than that portion below, and, becoming filled with drift, the river had only the drift filling to remove in modern times. This idea caused Dr. Pohlman to reduce the age of the falls to three thousand years. But almost universally the error of a deep preglacial