5>2 THE POPULAR SCIENCE MONTHLY. 



Lyell, in his " First Travels in the United States," have told us what 

 they thought the Falls are coming to. 



The reader will remember that the dip of the strata here is 20 

 feet a mile southward. He will remember, too, that the current below 

 the Falls is 15 feet a mile northward. If he will turn to the section it 

 may help him to see that a stratum which, a mile below the Falls, 

 crops out along the bank 35 feet above the river, would be brought 

 down, at the Falls, to the level of the river ; and he will see that, for 

 every mile the Falls have cut their way southward, they have lost 35 feet 

 in height the dip of the strata and slope of the channel. Let them cut 

 back two miles farther (this is the reasoning of Hall and Lyell), and 

 they will have passed the head of the Rapids. The shale which now 

 lies at their base and forms the lower part of the precipice will have 

 disappeared beneath the river-bed, and the limestone which has always 

 been at the top of the precipice will have reached the bottom. As the 

 Falls have receded by the action of the spray on the shale below, and 

 the breaking and falling down of the undermined limestone above, now 

 that the entire precipice is limestone, the features of the cataract will 

 begin to change. The rock will wear away faster at the top than at 

 the bottom, and the great Niagara only a hundred feet high now 

 will dwindle away into a succession of cascades and rapids. This is 

 the future as shaped in the minds of Hall and Lyell. They have over- 

 looked an important fact the change in the course of the river. 



A reference to the map will show that the American Fall (8) is cut- 

 ting eastward, and the Horseshoe (9) southward. But, after a few 

 hundred feet have been cut away, the direction of the Horseshoe will 

 change, and both Falls will move eastward. Above Goat Island they 

 will unite and move on, one Fall, of immense width, till Navy Island 

 cuts it in two. The greater Fall will then be on the American side, 

 and its recession will still be eastward. A little. Fall on the Canada 

 Bide will retreat southward around Navy Island and then Grand Island. 

 About a mile above the northern point of Grand Island this Fall will 

 have moved southward far enough to leave the shale and have the 

 precipice all of limestone. The water will then wear away the rim 

 faster than the base, and the Fall will become a series of cascades and 

 rapids. 



But the main Fall will have to cut back to within a mile of Tona- 

 wanda Island by the course of the river, nearly eight miles from the 

 Horseshoe before it makes the same southing. The Fall will have cut 

 back, not with the dip, but nearly at right angles across it. And by the 

 present rate of recession it must continue its work of excavation for 

 80,000 years before the shale will disappear under the bed of the river 

 and the limestone form the entire precipice. Then the same fate will 

 overtake this greater Fall which, ages before, awaited the other. All 

 this on the assumption that Nature is to go on selecting her own chan- 

 nels and seeking her own ends. 



