Science, Geology and Physics 



narrow, or has been much deeper in some parts than in others, 1889 

 the force of the water has been applied advantageously. 



There are many ways in which it is possible that the volume 

 of the river was made to differ at early dates from its present 

 volume. During the presence of the ice, there was a different 

 climate, and there were different drainage systems. 



Question 10. During the early history of the river, was the 

 annual rainfall on which its water supply depended greater or 

 less than now? 



Question 1 1 . Was the evaporation from the basin at that 

 time greater or less than now? It is believed that at the present 

 time the Niagara river receives less than half the water that falls 

 upon its basin in rain and snow, the remainder being returned to 

 the air by evaporation from the lakes, from the surface of the 

 land and from vegetation. 



Question \2. Was the water supply increased by ablation? 

 There may have been times when the overlapping edge of the 

 glacier discharged to the Laurentian basin large bodies of water 

 furnished by the melting of ice that had congealed from the 

 clouds of regions far away. 



Question 13. Was the drainage area of the river at any time 

 increased through the agency of ice barriers? Just as the Win- 

 nipeg basin was made to send its water to the Mississippi, so we 

 can imagine that regions north of the Great Lakes and now 

 tributary to Hudson's bay, had their discharge temporarily 

 turned to Lake Superior and Lake Huron. 



On the other hand, we have seen that the discharge of the 

 whole district of the upper lakes was for a time turned away 

 from the Niagara river. Therefore, we ask: 



Question 14. To what extent and for what periods was the 

 volume of the river diminished through the diversion of the dis- 

 charge of the upper lakes? 



Assuming all these questions to be answered one by one, and 

 the variations of different sorts determined, it is still necessary to 



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