226 J. W. SPENCER POSTGLACIAL EARTH-MOVEMENTS 



this, the lower beach should reach an altitude at Montreal of about 645 

 feet, which is nearly 100 feet above the marine deposits found there, with 

 no corresponding shoreline. This further discredits any correlation of 

 the beach at the foot of Covey Hill, with marine deposits at Montreal. 11 



Present Stability of the Lake Region 



The measurements now obtained show that the deformation of the 

 region between the head of Lake Ontario and Parish ville amounts to 510 

 feet, or 680 feet if it be measured from the head of Lake Erie. Between 

 the outlet of Lake Huron and the highland, beyond the northeast angle 

 of Georgian Bay, nearly an equal amount has been found. These changes 

 have occurred since the birth of Magara Falls, which I have computed 

 at 39,000 years ago. A rise of somewhat more than 100 feet at the north- 

 east angle of Georgian Bay, in excess of that at the outlet of Lake Huron, 

 occurred since 3,500 years ago. 12 Let us see what is the status at the 

 present day. 



The intake of the Welland Canal (Port Colborne) is situated about 

 160 miles northeast of Cleveland, where at both places the daily fluctua- 

 tions of Lake Erie have been recorded for over fifty years. The post- 

 glacial rise between these points has been 120 feet. As the bench-marks 

 are permanent, any earth-movement should have become apparent in the 

 water level. I have taken the mean levels of each day for periods of five 

 years with the following results. For convenience in calculation the 

 water at Port Colborne was assumed to be 0.33 foot below the Cleveland 

 level. 



The mean difference of level recorded gives the following figures : 



Level at Port Colborne below that at Cleveland 13 



1855-1859. —.29 foot. 



1860-1865 +.07 " 



1866-1870 —.06 " 



1871-1875 —.13 " 



1876-1880 —.27 " 



1881-1885 —.26 " 



1886-1890 —.20 " 



1891-1895 —.26 " 



1896-1900 —.2,9 " 



1901-1905 —.28 •' 



1906-1910 —.24 " 



1011-1912 —.26 " 



11 Bull. Geol. Soc. America, vol. 23, 1912. 



12 J. W. Spencer : Evolution of the Falls of Niagara, etc., Geological Survey of Canada, 

 1907, p. 376. 



13 lb., chapter 31. 



