Science, CeologX) and Physics 



ward, in consequence of the dip of the rock in that direction. 1838 

 This cause has gradually lowered the waters of Lake Erie, and 

 will finally leave it entirely dry, except the channel of the river. 

 There is, however, no possibility of a great deluge occurring from 

 the sudden drainage of this lake, as stated by Mr. Lyell and other 

 geologists. 



If the southern shore of Lake Erie were formed by a vertical 

 wall of rock extending to the bottom, this catastrophe might be 

 apprehended ; but as it is, the bed of the lake where the Niagara 

 river leaves it is solid limestone, sloping south towards the centre. 

 We perceive, then, that the lake can be drained no faster than 

 this rock is worn off by the action of the water. The force of 

 the river is gradually decreasing, and of course the recession will 

 be more gradual from this cause. But for another reason, the 

 rate of recession will be incalculably less as we progress south- 

 ward. At the present time the falls recede principally by the 

 action of the water on the soft shale below, wearing it rapidly 

 away and leaving the limestone unsupported, when it falls of 

 its own weight. — After the falls recede about two miles farther, 

 the shale will have disappeared below the level of the river, and 

 consequently the water will descend over a solid wall of lime- 

 stone; after this period the falls will recede only by the slow 

 wearing of this rock. 



The accompanying woodcut represents a section of the rocks 

 at Lewiston. 1, the upper limestone; 2, shale; 3, limestone; 

 4, red marl and sandstone; 5, hard siliceous sandstone; 6, red 

 marl. The surface of No. 1 , at the top of the ridge, is worn 

 and scratched, as if by the action of running water, carrying with 

 it pebbles or hard materials. The shale, No. 2, is worn off at 

 a gradual slope; the limestone, No. 3, has its projecting surface 

 worn and scratched like the upper limestone. The hard sand- 

 stone, No. 5, projects much farther, and is also worn and 

 scratched. At the termination of this stratum is a small valley, 

 and beyond it a large mound of fragments of the sandstone and 

 two limestones; the former most abundant. These fragments 



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