256 THE HISTORY OF THE NIAGARA RIVER. 



may have been times when the overlappiug edge of the ghicier dis- 

 charged to the Laurentiau Basin hirge bodies of water furuished by the 

 melting of ice that had congealed Iroin 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 Winnipeg 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 dis- 

 trict 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 discharge of the 

 upper lakes ? 



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

 variations of dififerent sorts determined, it is still necessary to learn the 

 relations of those variations to each other, and so we ask : 



Question 15. How have the variations of rock section, the variations 

 of cataract height, the variations of form of channel, and the variations 

 of volume been related to one another in point of time? What have 

 been their actual combinations ! 



Question 10. How have the various temporary combinations of factors 

 affected the process of retreat and the rate of recession ? 



The tale of questions is not exhausted, but no more are needed if 

 only it has been shown that the subject is not in reality simple, as 

 many have assumed, but highly complex. Some of the questions are, 

 indeed, easily answered. It may be possible to show that others are 

 of small moment. It may even be that careful study of the local features 

 will enable the investigator to infer the process of cataract work at 

 each point from the existing condition of the gorge, and thus relieve 

 him from the necessity of considering such remote questions as the 

 nature of glacial climate and the history of glacial retreat. But after 

 all paring and pruning, what remains of the problem will be no baga- 

 telle. It is not to be solved by a few figures on a slate, nor yet by the 

 writing of many essays. It is not to be solved by the cunning discussion 

 of our scant, yet too puzzling, knowledge — smoothing away inconvenient 

 doubts with convenient assumptions and cancelling out, as though 

 compensatory, terms of unknown value that happen to stand on o|)po- 

 site sides of the equation. It is a problem of nature, and, like other 

 natural problems, demands the patient gathering of many tacts, of 

 facts of many kinds, of categories of facts suggested by the tentative 

 theories of to-day, and of new categories of facts to be suggested by 

 new theories. 



I have said our problem is but the stepping stone to another problem, 

 the discovery of common units for earth history and human history. 

 The Niagara bridges the chasm in another way, or, more strictly, in 



