124 



TRANSACTIONS OF THE CANADIAN INSTITUTE. 



[Vol v. 



A fact that should now be noted is that years of heavy precipitation 

 in the Lake Ontario region are not usually years of heavy precipitation 

 over the Upper Lakes and vice versa. To be convinced of this we have 

 only to inspect the following table, which shews the departures from 

 the average of twenty-five years in the various drainage areas, as obtained 

 from the yearly means at the stations before mentioned : 



It will be observed in comparing the Ontario and Superior departures 

 from average, that not only do the departures from average not agree as 

 to percentage above or below normal, but in 13 out of 18 years they 

 differ as to sign ; years with an excess of precipitation in one district 

 being years of deficiency in ):he other. A comparison of Lake Ontario 

 with Lake Huron shews a less marked difference, but even there it is 

 very pronounced. 



There being then such strong evidence that years of small precipita- 

 tion in the Ontario region are usually years of heavy precipitation over 

 the Upper Lakes, we may surmise that from 1834-46 was on the whole 

 a rainy period in the Upper Lake region. 



A glance at the lake level curves shews that obviously the seasonal 

 fluctuations are mainly attributable to the melting of the snow in the 

 spring, and to precipitation ; while streams are all full and evaporation is 

 not very great the lakes rise very rapidly, and then after midsummer, or 

 in the ca.se of Lake Superior after the end of August, fall steadily until 

 the melting of the snow in the following spring. 



The average annual range in feet of Lake Superior is 1.2, Lake Huron 

 1.3, Lake Erie 1.6, and Ontario 1.8. 



The curves shewing variation in annual rainfall, and the mean lake 

 levels, except that of Superior, are strikingly similar in form for the 

 greater portion of the period fpr which we have sufficient data, but 

 marked disagreements in some few years, and certain other features 

 shewn graphically on the charts indicate very clearly that, although the 

 level of each lake responds to an increased or diminished rainfall, there 

 are other factors to be considered. 



