290 Mr Forster on the Falls of the Niagara,- 



eighty-nine miles in length, and by a difference of elevation of 

 fifty-two and a half feet. 



As to the future rate of recession of the Falls, I believe it to be 

 equally difficult to speculate. It is very possible that long before 

 this vast wall of water advances to the brink of Lake Erie, it 

 will have totally altered its shape and aspect. As the Falls re- 

 treat, they also rise, obeying the general ascent of the land to- 

 wards Lake Erie, This circumstance, combined with the hori- 

 zontal position of the rocky beds which they intersect, gradually 

 reduces the thickness of the underlying section of shale, and 

 augments that of the overlying limestone. 



The diagram here annexed, will elucidate the arrangement 

 of the several strata along the river, and assist in displaying the 

 future positions which the Falls must occupy as they enter the 

 uppermost beds. 



O Lake Ontario ; E Lake Erie ; Q, Queenston ; G termination of the ra- 

 vine ; a the Falls seven miles from G ; b the probable future place of the 

 Palls when they will be in the strata c and d, and not, as at present, in d 

 and e\ c siliceous limestone, d geodiferous limestone, e friable shale. 



The vertical scale is of course greatly exaggerated beyond the 

 actual proportions, it being in all such diagrams impossible to 

 represent the distances and the heights in their true ratios. 



A still further retrogression will bring the cataract altogether 

 out of the inferior shale, the thickness of which at present is 

 ninety feet, and will cause the escarpment of the Falls to con- 

 sist only of the overlying limestone beds, and ultimately of a 

 still superior stratum, a tough siliceous limestone which occupies 

 the surface from Lake Erie down almost to the Falls. It seems 

 a plausible conjecture, that entering, as it thus certainly must, a 

 new series of beds possessing very different relations of hardness, 

 friability, and thickness, from those which compose the present 

 escarpment, both the rate and the mode of retrogression will be 

 materially modified. Should the upper stratum, instead of be- 

 ing, as it now is, the hardest, become, as it possibly may, be. 



