Septembeb 18, 1908] 



SCIENCE 



383 



trict has risen approximately 700 feet since the 

 beach was formed. 



If we restore the district near the Nipissing 

 pass to the position which it had at the Algon- 

 quin stage, by lowering it 700 feet below its 

 present position, we put the floor of the Nipissing 

 pass (which is now less than 700 feet A. T.) a 

 little below sea level. This suggests the possi- 

 bility that the sea may have entered the basins 

 of the Great Lakes from this direction. 



The conjectured altitude of Lake Algonquin, 

 600 feet A. T., is attributed to an ice barrier 

 over the Nipissing pass. It is very probable that 

 this barrier persisted imtil the floor of the pass 

 had been raised well above sea level, by the dif- 

 ferential uplifts which produced the diverging 

 series of beaches below the Algonquin. If the 

 sea did come in through the Nipissing Pass, how- 

 ever, a record of it might be expected in raised 

 beaches north of the pass. 



Professor Goldthwaite was followed by Dr. J. 

 W. Spencer, who presented the two following 

 papers, both of which were illustrated by lantern 

 slides. 



Changes in the Recession of the Falls of Niagara. 



The following is a mere summary of some of 

 many chapters required in describing phenomena 

 which bring to light the changing features of 

 Niagara Falls. 



From my own measurements of the recession 

 of Niagara Falls, compared with those of Hall 

 in 1842, I find that the average rate is 4.2 feet a 

 year for the width of the canyon (1,200 feet) 

 made by the cataract; and from the discovery of 

 its position in 1678, approximately the same rate 

 formerly prevailed. 



From a point 1,100 feet below the apex of the 

 falls, to the Whirlpool, I find by my new sound- 

 ings, that the depth of the gorge reaches to the 

 same plane of 86 to 92 feet below the level of 

 Lake Ontario, when allowance is made for the 

 descent of the river surface at the Whirlpool 

 Rapids, where borings show that the canyon was 

 trenched to the same depth as above and below 

 them by the falls. But soundings, which I suc- 

 ceeded in making immediately below the falls 

 themselves, prove that the cataract can excavate 

 to a depth of not over 100 feet below the river 

 surface, consequently the present deep channel of 

 186 to 192 feet could have been made only when 

 the falls were higher — that was before the gorge 

 at the Whirlpool Rapids had become partly re- 

 filled by the recent falling of the adjacent wall- 

 rocks. At this section, for a short time, the vol- 



ume of the river was diminished by the tem- 

 porary partial diversion of the Upper Lake drain- 

 age, by way of Chicago. Until the falls had 

 crossed the Lyell ridge, about a mile and a half 

 below their present site, they were somewhat 

 higher than now. By the trenching of this ridge 

 the surface of the river was lowered by about 

 sixty feet, on account of the removal of the drift 

 from the pre-glacial valley, which they took pos- 

 session of, whereupon the Upper Rapids came into 

 existence. The site of the Whirlpool was the head 

 of a pre-glacial canyon, above which was a small 

 tributary heading in the Lyell ridge, two miles 

 away, since deepened by the falls. Below the 

 whirlpool to the head of Foster's Flats (about 

 two thirds of a mile), the gorge is similar to that 

 above, and here there was a slight change in the 

 height of the falls, as explained. Throughout 

 ttiese four miles the greater height of the falls 

 increased the rate of recession. By differentiating 

 the work of the falls at each point, the time 

 required for the formation of this longitudinal 

 stretch of the gorge is now computed to have 

 been 3,500 years only. 



The history of the lower three miles is entirely 

 different. At their birth, the falls were only 35 

 feet high — shown by a terrace at the mouth of 

 the gorge. From time to time the falls increased 

 in height as the Ontario waters retreated to 

 lower levels, even to 180 feet below the level of 

 the present day— shown by the deep inner channel 

 revealed by my recent soimdings. The falls then 

 reached over 500 feet in height, but consisted of 

 three separate cataracts, the lowest of which was 

 over 300 feet high; however, its work as rapids 

 was exhausted in excavating a new channel for 

 over eleven miles beyond the end of the gorge, 

 while the upper cataracts were already far ad- 

 vanced within the canyon. Shortly after the third 

 cataract, now a fall, had receded half a mile 

 within the gorge, its height was reduced by nearly 

 180 feet, owing to the rising of the Ontario waters, 

 due to the warping of the earth's crust at the 

 outlet of the lake. 



The second cataract gained upon the upper one, 

 imtil the two imitfjd at a well-marked point at 

 Foster's Flats, less than three miles from the 

 mouth of the gofge. At this time they had each 

 reached about 120 feet in height. A few hundred 

 feet beyond this point, at the head of the flats, 

 occurred the most remarkable change in the his- 

 tory of the river. Until this time the volume of 

 the river was only that of the Erie drainage, the 

 three upper lakes emptying to the northeast, as 



