and the Reasonings of some Authors respecting them. 289 



ritlge, where the Delaware traverses the same mountain in Penn- 

 sylvania, to form the lovely scenery of the Water-Gap, and in- 

 deed in twenly other cases which might be cited. An arrange- 

 ment of our plains in successive plateaus is by no means fre- 

 quent, and neither Trenton Falls, nor those of the Gennessce, 

 have resulted from any such structure of the surface. 



Mr Fairholme has the following passage : " If this point be 

 admitted," (the recession of the Falls), " it is equally obvious 

 that a continuation of the action must occasion a continuance of 

 the effect, and that a time must consequently arrive, when the 

 whole barrier between the lakes must be intersected. This pe- 

 riod is, of course, very remote; but it is not the less certain and 

 unavoidable, if the causes now in force continue to exist. The 

 consequences will be most extensive and disastrous, more so, in- 

 deed, than any natural event within the range of history. The 

 whole of the upper lakes of North America, which more resem- 

 ble seas than inland collections of fresh water, will then be low- 

 ered by nearly three hundred feet, and the low countries be- 

 tween Lake Ontario and the Atlantic can scarcely escape from 

 being swept at once into the ocean."* 



To prove that this is too alarming a picture, it is only neces- 

 sary to add to the fact, that no barrier, properly speaking, in- 

 tervenes between the present cataract and Lake Erie, the bot- 

 tom of which shelves very gently from the shore, and is nowhere 

 deep, averaging only one hundred and twenty feet. The action 

 of discharge must therefore at all times, even long after the ca- 

 taract shall have entered the lake, be extremely gradual, as M. 

 De la Beche has amply shown.-f* Besides, even supposing it 

 possible for Lake Erie to empty itself thus suddenly, no similar 

 discharge could take place from the other lakes, inasmuch as 

 Lakes Huron and Michigan are cut off f>oni Erie by a livcr 



• The distance being twenty -one miles from the jiresent cataract to Lake 

 Erie, and the rate of action being about four feet per annum, the time neces- 

 sary for this great natural operation will be 27,720 years. As the Fall will, 

 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 may therefore safely reckon on a lease of from 30,000 to 40,000 

 years Fairholme. 



f Third edition of Manual, p. ICO. 



