NIAGARA AS A TIMEPIECE. 



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

 in Fig. 16. 



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 sup- 

 posed that it indicated 

 an ancient course of 

 the river itself, which 

 extended thence to 

 the St. Davids' Val- 

 ley, about four or 

 five miles distant, al- 

 though the country 

 forms a level floor 

 which told of no bur- 

 ied channel (see Fig. 

 5). This mistake arose 

 from the perpendicu- 

 lar walls of the whirl- 

 pool basin, without the 

 necessity of sloping 

 sides for ancient val- 

 leys being then per- 

 fectly known, and 

 without the author evi- 

 dently going through 

 the ravine where rocks 

 were exposed. The se- 

 rious feature of the 

 mistake was that it led 

 to the supposition that 

 perhaps much of the 

 gorge above the whirl- 

 pool was older than 

 that portion below, 

 and, becoming filled 

 with drift, the river 

 had only the drift fill- 

 ing to remove in mod- 

 ern times. This idea 

 caused Dr. Pohlman to reduce the age of the falls to three thou- 

 sand years. But almost universally the error of a deep preglacial 



^AGAEA 



Grass Id. 



Fig. 9. Map op the Niagara Gorge (United States Lake 

 Survey), showing its Variable Width and Cross- 

 sections. 



