WATERS OF THE LAKES. 249 



various places. How high the lake may rise, when it 

 next begins to increase, past experience does not enable 

 us to judge. As we are ignorant of the cause, we 

 cannot say to what level a rise is possible in existing 

 circumstances*, we cannot, therefore, reason as to the 

 cause or antiquity of the ancient lake-beaches, especially 

 those which are not greatly elevated above the present 

 waters, or draw safe conclusions as to the permanent 

 change of level which the lakes may now be presumed 

 to have undergone. Hence these oscillations in the 

 lake-levels have been subjects of inquiry and discussion 

 both by Mr Hall, one of the geologists for the State of 

 New York, and by Mr Hlggins, of the geological survey 

 of Michigan. 



Variations in the fall of snow and rain in the lake 

 country, and differences in the amount of evaporation, 

 suggest themselves as the simplest causes of the pheno- 

 mena. But such causes — unless, in this region, they act 

 in obedience to some steady alternating law — will not 

 explain the specialties of the case. The rise and fall of 

 the lake-levels are so gradual, and continue to augment 

 for so long a period, that a steady and increasing aug- 

 mentation of the water poured into the lakes must go 

 on while the level is rising, and a similar gradual and 

 long-continued diminution while it is falling. Meteoro- 

 logical observations have not yet shown that such aug- 

 mentations as these of the fall of rain and snow, or of 

 lake evaporation, do take place in any part of the world. 



The quantity of water which escapes from the lake 

 by its natural outlet, the Niagara Eiver, is an important 

 fact in this discussion. The Falls of Niagara, during 

 the high-water of summer, allow 20,000,000 o.*^ cubic 

 feet to fall over them* — a discharge which, taking the 

 area of Lake Erie at 10,000 miles,t would lower the 



* This is Mr Barrett's, the latest and best determination. 

 + Dr Houghton estimates it at 9600 square miles. 



