Reviem—Dr. J. W. W. Spencer — The Falls of Niagara. 315 



II. — The Falls op Niagaka, thkir Evolutio^t and varying Eelations 

 TO THE Great Lakes; characteeistics of the poaver, and the 



EFFECTS of ITS DIVERSION. By JoSEPH WiLLIAM WiNTHROP SpENCEK, 



M.A., Ph.D., F.G.S. 8vo ; pp. xxxi, 490, with large map (in 

 pocket), 43 other maps and pictorial plates, and 30 text-figures. 

 Ottawa, 1907. 



THIS monograph on the geology and physics of Niagara Falls was 

 prepared under a commission from Dr. Robert Bell, Acting 

 Director of the Geological Survey of Canada, and it has been issued 

 under the Department of Mines connected Avith that establishment. 



The leading conclusions of the author were brought last year before 

 the British Association, and were printed in the Geological Magazine 

 for 1907 (pp. 440-1). "We have now the satisfaction of calling 

 attention to the completed work, in which the details of Dr. Spencer's 

 long-continued and painstaking researches are published. 



Lyell, during his visit to Niagara in 1841-2, came to the conclusion 

 that the average rate of erosion of the chasm below the falls had been 

 about one foot annually, and that " it would have required 35,000 

 years for the retreat of the Falls, from the escarpment of Uueenstown 

 to their present site." At the same time, as he pointed out, " we 

 cannot assume that the retrograde movement has been uniform."^ 



These views are to a certain extent confirmed by Dr. Spencer, who 

 estimates a total of 39,000 years as the age of the Falls, but he differs 

 materially from Lyell in the evidence he brings forward to show that 

 the recession of the first three miles occupied 35,500 years, and of the 

 last four miles only 3,500 years. 



Dr. Spencer now claims that " The recession of the Falls, from 

 their birth to the present day, and for the future, has been determined, 

 as well as their age." His investigations include soundings at all the 

 changing points of the gorge, borings to ascertain the character of 

 buried channel-beds, surveys of the old river banks, and observations 

 on lake fluctuations. Thereby has he been enabled to estimate the 

 changes that have occurred at different periods in the volume and 

 currents of the river, and in the height of the Falls ; gatheiing evidence 

 from a study of the buried vallej^s, and of other phenomena that have 

 influenced erosion far from the great cataract. Thus he concludes that 

 originally the overflow from Lake Erie alone was discharged over the 

 Falls, and progress in excavation was comparatively slow. Through 

 subsequent earth-movements the drainage of Lakes Huron, Michigan, 

 and Superior was added, and erosion was intensified. 



The upper part of the Niagara (iforge has been excavated along the 

 line of a pre-Glacial feature, within which the drainage was formerly 

 in the opposite direction to that of the present day. The account 

 given by the author of this " Falls- Chippawa channel " is, he believes, 

 the first suggestion of its existence. Out of this trough the falls 

 are now beginning to emerge, with consequent retardation of their 

 recession. 



1 " Principles of Geology," 11th ed. (1872), vol. i, pp. 356, etc. 



