450 Spencer 1 — Another Episode in the History of Niagara. 



would have been quickly reexcavated by the current easily 

 removing the drift tilling. With the channel being thus deep- 

 ened so rapidly, in loose material, it would cause a concentra- 

 tion of the current within a narrow gorge, and materially 

 augment the mechanical effects upon the floor of the cafion 

 — thus deepening without broadening the chasm. Indeed, is 

 not this feature of the contraction of the canon perfectly 

 developed at the outlet of the whirlpool, where the whole vol- 

 ume of drainage of all the upper lakes, by Niagara River, 

 rushes, as out of a waste weir, through a channel only 400 

 feet wide, with an estimated depth of 50 feet? Tims there 

 seems no reason to suppose that the volume of the river was, 

 during this episode, reduced to one-fourth or one-fifth of the 

 present amount, — as would have been the case with Mr. Tay- 

 lor's hypothesis, especially as the work of the Falls would have 

 been greatly diminished by the reduced descent of its waters 

 (as already described on page 445). 



A partial reduction of the volume of the water, at this time, 

 was more than probable, but from another cause than that here 

 discussed. In the " Duration of Niagara Falls,"* it was 

 shown that the Johnson ridge caused the waters of the Erie 

 basin to rise to the point of discharging a portion of the waters 

 of the upper lakes into the Mississippi, by way of a new 

 outlet near Chicago. But the falls dissected Johnson ridge 

 before there was an extensive drainage of the Niagara waters 

 to the Mississippi ; whereupon there was a lowering of the 

 upper lakes below the Chicago overflow. At this distant day, 

 it is difficult to estimate the exact amount of such discharge 

 which may have been greater than at first supposed. The ter- 

 races or shore-lines in the St. Clair outlet of Lake Huron, at an 

 elevation of fifteen or twenty-five feet above the level of Lake 

 Erie, apparently correspond with the level of the Erie waters, 

 as they were being raised by the Johnson ridge before it was 

 dissected by Niagara Falls. Thus the deserted shore-lines of 

 the lakes support the evidence of the partial drainage, at this 

 time, of the upper lakes into the Mississippi. 



The physical conditions as now described account more fully 

 for the narrows of the gorge than any previous explanation, 

 as the cause of its shallowness seems to have been made clear. 

 This solution of a condition previously overlooked may possi- 

 bly be found entirely sufficient, and it has an advantage of 

 being in full accord with mechanical forces which we see at 

 work in Niagara to-day. The new discoveries in the history of 

 Niagara River, which have here brought 'about a revision of 

 the episodes, will somewhat alter the estimate of the age of 

 the Falls from 32,000 years, but whatever figures result they 

 will doubtless approach more nearly the true age of the Falls. 



* Cited before. 



