as illustrating the Geology of North America, 15 



causes now in force continue to exist. The consequences 

 will be most extensive and disastrous, more so, indeed, than 

 any natural event within ihe range of history. The whole of 

 the upper lakes of North America, which more resemble seas 

 than inland collections of fresh water, will then be lowered 

 by nearly 300 feet, and the low countries between Lake On- 

 tario and the Atlantic can scarcely escape from being swept 

 at once into the ocean. 



But it is not my present object to look at this subject pro- 

 spectively. We shall find the retrospect equally distinct, and 

 infinitely more instructive, and I shall therefore now resume 

 that view of the matter. 



No one who has examined and described the phenomena 

 of Niagara has ever doubted that the section of the strata has 

 been effected by the sole action of the continued current; and 

 we have only to consider the nature of the existing causes 

 and effects, as exhibited at the cataract and below it, to be 

 convinced that this is unquestionably the case. Had this cele- 

 brated fall been situated in the Old World, — for example, in 

 Italy, in India, or in Egypt, — we should have been enabled to 

 calculate with precision the rapidity of its retrograde move- 

 ment, by means of the ancient temples and other buildings 

 which would probably have marked its former site in remote 

 periods. Not having this advantage, however, and finding it 

 situated in a region which, but a century ago, had never been 

 visited except by the hunter or the roving Indian, we are com- 

 pelled to adopt as a basis for our calculation the observed 

 effects now in daily progress, and the evidence of respectable 

 individuals who have resided for the last 40 or 50 years in 

 the immediate neighbourhood of the spot. 



When Captain Hall was informed, by authorities upon which 

 he could confide, that the cataract had receded about 50 yards 

 in the last 40 years, he found great difficulty in giving credit 

 to so rapid an action, being little short of kfect per annum : 

 and he was consequently led to a minute examination of the 

 nature of the rock and the direction of its stratification, when 

 he at once perceived and admitted that this rate of action had 

 probably not been over stated. He describes the rock as 

 calcareous, and the stratification as quite horizontal, as is usual 

 with such secondary formations. Near the top, the stone is 

 hard, but as the examination is carried downwards, the solid 

 stone ceases, and a crumbling shale succeeds at the depth of 



however, be higher than it now is when it reaches the top of the rapids, 

 the action cannot be calculated at so much as it now is, and the United 

 States on the coast mav therefore safely reckon on a lease of from 30,000 

 to 40,000 years. 



