250 PEOBABLE CAUSE OF THIS CHANGE. 



level of the lake one foot in ten days ; or, more cor- 

 rectlj, if Niagara were dammed up, the level of the 

 whole lake would be raised two feet in ten days — one foot 

 by the usual supply of water poured into the lake from 

 above, and another by the water prevented from escap- 

 ing. Any sudden increase in the fall of rain or snow, 

 therefore, would soon run off, and leave the lake at its 

 usual level. 



If we consider the case of Lake Erie by itself, and 

 compare its area of 10,000 square miles with that of 

 all the upper lakes united, which cover 77,000 square 

 miles, and suppose these upper lakes to be raised very 

 high by one extraordinary fall of rain or snow, or by 

 a great diminution in the evaporation of one short 

 cold summer, then it is possible that the discharge from 

 these upper lakes of this one unusual amount of water 

 might, by the nature of the outlet into Lake Erie, be so 

 regulated as to continue augmenting for a series of 

 years, and again, as it lessens, to continue diminishing 

 for another series. But this possible explanation seems 

 to fail, when it is recollected that Lake Michigan itself, 

 one of these upper lakes, exhibits similar oscillations of 

 level. The source of the increased or diminished supply 

 must, therefore, be sought for in Lake Superior, if this 

 be considered a probable cause. But, unfortunately, 

 the remoteness and hitherto generally wilderness state 

 of the shores of this lake have prevented any obser- 

 vations being made, by which light could be thrown 

 on this interesting point. 



Part of the country through which the railway con- 

 ducted us on our way to Niagara was still uncleared or 

 unstumped, and sprinkled with log-huts and apparently 

 poor settlers, surrounded by indifferent crops of Indian 

 corn, on soils evidently better adapted for wheat. We 

 cross again, on this route, the belt of flat wheat-land, 

 belonging to the Onondago salt and Niagara limestone 



