Lundy Beach and Birth of Lake Erie. 211 



40 feet above the Erie level. Thus it becomes apparent that 

 the elevation of about the last 20 feet has taken place 

 since the recession of the falls past the Johnson ridge, for 

 otherwise such a large river with a great breadth would have 

 emptied the lakes and the recession of the falls must have 

 ceased. That the water was recently higher about the head 

 of Lake Michigan than now, the swampy flats bear witness, and 

 the low lands continue far southward so that the rocky floor of 

 the country — only 7 feet above the lake level (Ossian Guthrie) 

 is 25 miles distant from the lake. Over this extensive plain, 

 the low country has been a swamp, and drained sluggishly in 

 both directions whilst silting over, to the extent of a few feet, 

 the rocky floor of the country. But the entire drainage of 

 Lake Michigan to the southwest could not have been estab- 

 lished. The lowering of the water by a few feet in the Michi- 

 gan basin as well as in the Erie has been produced by the 

 recession of the falls past the Johnson ridge. 



From the modern rate of the recession of the falls, which is 

 about four feet a year, and the distance of 6,000 feet which 

 the falls have receded, since passing the Johnson ridge, we 

 find that the terrestrial warping in the vicinity of Niagara 

 Falls could not have exceeded 21 feet in 1500 years, or 1*5 feet 

 a century. But with the silting up of the Chicago (more cor- 

 rectly Lemont) overflow not more than 20 feet (or possibly 15 

 feet if the waters were deeper) of the last uplift of the John- 

 son ridge have been developed since the recession of the falls 

 through that ridge. Thus the rate of terrestrial deformation 

 or uplift in the Niagara district does not exceed 1*25 a century, 

 with a possible reduction to one foot in the same time, if the 

 secular rate were uniform. But there have doubtless been 

 episodes of rest and others of uplift so that the actual rate 

 of movement might have been more rapid, but the above esti- 

 mate is the average during these times of elevation and inter- 

 vening repose. 



The agents of the deformation in the Erie basin have not 

 been so continuous or so active as in other portions of the lake 

 region ; but if a mean rate for long" epochs can be taken as 

 here indicated, then nearly 13,000 years* have elapsed since 

 the Lundy beach commenced to be deformed. The Iroquois 

 beach is however more accurately measured. In the vicinity 

 of the outlet of Lake Ontario, the deformation is double that 

 in the Niagara district. At that outlet, the tilting has 

 amounted to 370 feet by the post-Iroquois movement, and at 

 2*5 feet a century about 14,800 years have elapsed since the 

 close of the episode of the formation of that deserted shore 

 line. The conjectural mean deformation over long epochs 



* 160 feet divided by 1 to ]-25 feet a century. 



