440 Spencer — Another Episode in the History of Niagara. 



time descended only 200 feet in place of 326 feet, as to-day ; 

 (3) that Foster's flats recorded the amount of recession of the 

 Falls during the earlier stages, when the Erie waters alone 

 drained through Lake Erie, and cascaded over a diminished 

 fall ; (4) that when the Falls had receded to Foster's flats, all 

 the drainage of the upper lakes was turned into Niagara River ; 

 (5) that again the descent of the river was increased to 420 

 feet (as first shown by Prof. G. K. Gilbert), which increase 

 gave rise to a succession of cascades, after which the height 

 was supposed to have been directly reduced to the present level. 

 The most important and continuous of these cascades was that 

 over the Medina sandstone, still represented by rapids ; and it 

 may be most properly named the Gilbert Falls. 



These changing conditions in the physics of the river nec- 

 essarily greatly modified the rate of recession of the Falls, and 

 from their considerations, a new determination of their age 

 became necessary. These calculations were only a stepping 

 stone towards ascertaining the age of the Falls, and each addi- 

 tion to our knowledge of the various phases of the river will 

 enable us to approach a more accurate computation of the dura- 

 tion of the Falls. There was also brought to light for the 

 first time a means of determining the rate of the upward move- 

 ment of the earth's crust, and the evidence of the extinction 

 of the Falls by the diversion of the waters of all the upper 

 lakes into the Mississippi by way of Chicago. 



However, all the physics of the river were not satisfactorily 

 explained. Thus the section of the canon, about 4,300 feet* 

 long, at the Whirlpool Rapids, is the narrowest and shallowest 

 part of the gorge, not explicable by a changing character of 

 the rock. Even the provisional explanation of the writer was 

 not satisfactory to himself, and accordingly another was offered 

 by Mr. F. B. Taylor, which will be noted later. Subsequently, 

 Prof. Gilbert estimated various depths of the river channel, f 



ing of the American Association for the Advancement of Science in 1888, of 

 which an abstract appeared in the Proceedings of the Society for that year. 



That which Air. Gilbert had written was as follows: "The rate " (of recession 

 of the Falls) "may also have been influenced ... by variation in the amount of 

 its volume " (i. e. of the Niagara River) " due to change of climate or catchment 

 basin. The catchment basin was formerly extended by including parts of the 

 area of the ice sheet. It may have been abridged by the partial diversion of the 

 Laurentian drainage to other courses " (Proc. A. A. A. Sc, vol. xxxv, p. 223. 

 1886). This is the entire statement, implying the possibility of changes of outlet 

 in any direction being a subject for consideration, and does not advance the dis- 

 covery or hypothesis as stated by Mr. Taylor, although it announces the hypothesis 

 of an increased discharge from glacial waters. 



* Originally only a length of 4,000 feet was taken. 



f See American Geologist, vol.xviii, pp. 223, 1896. The maximum depth of the 

 river had been found by soundings to reach 189 feet in the basin just below the 

 modern falls; and 96 feet in depth immediately outside the end of th9 gorge. 

 Mr. Gilbert estimated the depth of the whirlpool rapids at 35 feet; of the whirl- 

 pool, 150 feet ; of the channel at outlet of whirlpool at 50 feet ; of the basin 



