J. W. Spencer — Duration of Niagara Falls. 459 



4. Ancient Topography and Basement. 



In the numerous writings upon the Niagara river one 

 ancient topographic feature has been overlooked and another 

 exaggerated into importance which it does not possess. The 

 ancient drainage of the Erie basin was not by way of the 

 Niagara but by a channel forty miles to the west.* Even at 

 the end of the Lake Erie the borings show old channels 

 deeper than the floor of the river across the Devonian escarp- 

 ments, f 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 basement 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. 11). 

 This depression is part of the ancient Tonawanda basin, which 

 is now filed with drift (see fig. 8). The gorge through John- 

 son'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 

 (w, fig. 3), in the line of the extension of the St. David's val- 

 ley. This forms an embayment one and a 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 con- 

 sequently 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. 





Fig. 2. — Map of the whirlpool ravine ; bb, position of section (fig. 3). 



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 Y-shaped bound- 



* " Origin of the Basins of the Great Lakes," Q. J. G. S. Lond., vol. xlvi, p. 

 523, 1890, and "Notes on the Origin and History of the Great Lakes," Proc. A. 

 A. A. S., vol. xxvii, 1888. 



f " The Life History of Niagara," by Julius Pohlman, Trans. Am. Inst. Min. 

 Eng. 



