146 Dr. J. W. Spencer. Niagara Falls [June 7, 



4. Ancient Topography. The Niagara is a modern river. It crosses 

 a broad ancient valley nearly 100 ft. deep, in the vicinity of the Falls. 

 This depression has largely escaped the attention of even geologists, 

 and entirely in its bearing upon the history of the Falls. The pecu- 

 liar extension of the chasm at the Whirlpool, and the buried valley of 

 St. David's, have been considered by many as part of a preglacial 

 Niagara river. This is now found to be a branch of a buried valley 

 outside the Niagara canon, and hundreds of feet shallower, with 

 ancient sloping \/-shaped walls, whilst those of the gorge are vertical. 

 It is only an incident that the modern river touched this drift-filled 

 valley, but it has given rise to the elongation of the chasm at the 

 Whirlpool. The drainage of the tableland in ancient times was across 

 the direction of the Niagara river, and was strongly marked by bold 

 limestone ridges, which have only been penetrated by the Falls in 

 modern times. Even the Erie basin emptied by a route several miles 



west of the Niagara. 



5. Basement of the River. In order to explain the work done by 

 the river, this feature is described, part of the banks of the original 

 course, before sinking into the chasm, being on hard rocks, and part 

 on local deposits of drift. Even the deserted river banks carved out 

 of such accumulations are still well preserved. 



6. Discharge of the Niagara River. This is only important in order 

 to learn what is the discharge of the Erie basin alone ; for during a 

 considerable portion of the life of the Niagara only the Erie waters 

 fell over the falls. The drainage of the Erie basin is 3/11 of that 

 of the four great upper lakes. 



7. Modern Recession of the Falls. From four surveys, extending 

 over a period of forty-eight years, the mean modern rate of recession 

 of the Falls is found to be 4'175 ft. a year. Its rate is variable with 

 secular episodes of rapid medial recession, followed by its cessation along 

 the axis, but with increased lateral retreat. This cycle appears to 

 take about fifty years. But the detailed figures are given with a map. 

 This rate is, however, excessive, on account of the geological con- 

 ditions favouring the rapid modern recession, but the rate taken for 

 the mean recession under the conditions of the modern descent of 

 the river with the present discharge is 3' 75 ft. a year. 



8. Sketch of the Lake History and the Nativity of Niagara River. 

 At one time a great proportion of the lake region was covered by a 

 single sheet, or the Warren Water. Upon its dismemberment in part, 

 at least, by the rise of the land one large lake was formed occupying 

 the basins of Huron, Michigan, and Superior ; and another a portion 

 of the Erie extending into the Ontario basin. The waters in these 

 two basins were subsequently lowered, so that they fell to their rocky 

 eastern rims, and the three upper lakes discharged by way of Lake 

 Nipissing and the Ottawa river, and the Niagara had its birth, 



