Science, Geology and Physics 



by a channel 40 miles to the west. Even at the end of the Lake 1895 

 Erie the borings show old channels deeper than the floor of the 

 river across the Devonian escarpments. The feature overlooked 

 is the Tonawanda valley, a mile and a half in width, extending 

 from the rapids above the falls to the Johnson ridge. Its base- 

 ment is 80 or 90 feet below the northern barrier of Johnson's 

 ridge. The rocky sub-surface of Goat Island was part of the 

 ancient floor (see fig. 27). This depression is part of the ancient 

 Tonawanda basin, which is now filled with drift (see fig. 24). 

 The gorge through Johnson's ridge is modern with vertical 

 walls, but half a mile to the west it falls away and the wells 

 reveal the continuation of the Tonawanda depression extending 

 northward. It is again made known by a well half a mile west 

 of the whirlpool ( n\ fig. 19), in the line of the extension of the 

 St. David's valley. This forms an embayment one and half 

 miles wide and only three-quarters of a mile deep in the face 

 of the Niagara escarpment. The modern river is simply crossing 

 a portion of the old Tonawanda basin in the vicinity of the 

 falls, and consequently it has here much less rock to excavate 

 than through and north of Johnson's ridge. 



The other feature is the imaginary whirlpool — St. David's 

 valley, supposed to have been the old course of the river. Above 

 and below the whirlpool alike, the gorge is of recent date as may 

 be seen by the vertical walls shown in the several sections. The 

 whirlpool ravine has sloping V-shaped boundaries in its higher 

 portion, which is an antique structure. The depression is so 

 obstructed with drift, that gives rise to landslides that the old 

 topography is much obscured. Yet a little stream has removed 

 the fallen earth and exposed a natural section of Clinton lime- 

 stones, which cross the valley at an elevation of 1 1 5 feet above 

 the surface of the whirlpool, or 160 feet above Lake Ontario, 

 with Niagara shales showing for at least 20 feet higher. Thus 

 the rocky barrier across the ravine is not less than 240 feet above 

 the bottom of the canon in the whirlpool. This barrier in the 

 ravine is illustrated in fig. 19, which should be compared with 



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