Science, Geology and Physics 



According to this hypothesis, the Falls must have had originally 1841 

 nearly twice their present height, and must have been always ye 

 diminishing in grandeur from age to age, as they will continue 

 to do in future so long as the retrograde movement is pro- 

 longed. It becomes, therefore, a matter of no small curiosity 

 and interest to inquire at what rate the work of excavation is now 

 going on, and thus to obtain a measure for calculating how many 

 thousands of years or centuries have been required to hollow out 

 the chasm already excavated. 



It is an ascertained fact, that the Falls do not remain abso- 

 lutely stationary at the same point of space, and that they have 

 shifted their position slightly during the last half century. Every 

 observer will also be convinced that the small portion of the 

 great ravine, which has been eroded within the memory of man, 

 is so precisely identical in character with the whole gorge for 

 seven miles below, that the river supplies an adequate cause for 

 executing the task assigned to it, provided we grant sufficient time 

 for its completion. 



The waters, after cutting through strata of limestone, about 

 fifty feet thick in the rapids, descend perpendicularly at the Falls 

 over another mass of limestone about ninety feet thick, beneath 

 which lie soft shales of equal thickness, continually undermined 

 by the action of the spray driven violently by gusts of wind 

 against the base of the precipice. In consequence of this disinte- 

 gration, portions of the incumbent rock are left unsupported, and 

 tumble down from time to time, so that the cataract is made to 

 recede southwards. The sudden descent of huge rocky frag- 

 ments of the undermined limestone at the Horseshoe Fall, in 

 1828, and another at the American Fall, in 1818, are said to 

 have shaken the adjacent country like an earthquake. Accord- 

 ing to the statement of our guide in 1841, Samuel Hooker, an 

 indentation of about forty feet has been produced in the middle 

 of the ledge of limestone at the lesser fall since the year 1815, so 

 that it has begun to assume the shape of a crescent, while within 

 the same period the Horseshoe Fall has been altered so as less to 



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