Science, Geology and Physics 



and others concerning eastward outlets from the upper lakes, sub- 1903 

 trading their flow from the Niagara river, which, as I believe, u P h * m 

 are untenable, or at the most, had only a very short existence. 

 Omitting that element of the problem as insignificant, we have 

 approximately 7,000 years, according to diverse but concurrent 

 computations, for the probable time occupied in the erosion of 

 the gorge. 



Not satisfied with rejecting the hypothesis of long and great 

 subtraction from the water supply at Niagara, I wish to direct 

 attention to a very important cause of great increase of size of 

 the river and falls at the beginning of the gorge erosion. The 

 discharge of the river during the last 1 ,000 years may be approxi- 

 mately represented by 1 ,200 or 1 ,500 feet of water covering all 

 the upper St. Lawrence drainage basin above these falls. This 

 average water supply I believe to have been doubled or trebled 

 during the first 1 ,000 years of the river history by the added flow 

 derived from the final melting of the ice-sheet, mostly 3,000 to 

 5,000 feet or more in thickness, upon a very large region stretch- 

 ing from Lakes Huron and Superior far north and northwest. 

 For some part of this time the Niagara river probably received 

 the outflow from the basin of the glacial Lake Agassiz, that is, 

 the vast central tract of Canada between James Bay and the 

 Rocky Mountains. Within its first 1,000 years, therefore, the 

 more powerful Niagara may have accomplished about half of its 

 gorge erosion between Lewiston and the whirlpool. When the 

 river was reduced to its present size, after its tributary ice-melting 

 ceased, 2,000 years were probably adequate for the completion 

 of the gorge to the whirlpool, the work having been greatly 

 lessened by preglacial erosion; similarly, on account of the old 

 St. David's ravine, 1 ,000 years, or less, would suffice for the 

 erosion along the whirlpool rapids; and, under the present con- 

 ditions of gorge cutting, 3,000 years were required for the last 

 two miles. The whole history would thus comprise about 7,000 

 years. 



This measure, which (not to be too exact in figures depending 



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