NIAGARA 205 



series of longitudinal protuberances and furrows which 

 act like cylindrical lenses, introduces variations in the 

 intensity of the light, and materially enhances its beauty. 



We have now to consider the genesis and proximate 

 destiny of the Falls of Niagara. We may open our way 

 to this subject by a few preliminary remarks upon erosion. 

 Time and intensity are the main factors of geologic change, 

 and they are in a certain sense convertible. A feeble 

 force acting through long periods, and an intense force 

 acting through short ones, may produce approximately 

 the same results. To Dr. Hooker I have been indebted 

 for some specimens of stones, the first examples of which 

 were picked up by Mr. Hackworth on the shores of 

 Ly ell's Bay, near Wellington, in New Zealand. They 

 were described by Mr. Travers in the "Transactions of 

 the New Zealand Institute." Unacquainted with their 

 origin, you would certainly ascribe their forms to human 

 workmanship. They resemble knives and spear-heads, 

 being apparently chiselled off into facets, with as much 

 attention to symmetry as if a tool, guided by human 

 intelligence, had passed over them. But no human in- 

 strument has been brought to bear upon these stones. 

 They have been wrought into their present shape by the 

 wind-blown sand of Ly ell's Bay. Two winds are domi- 

 nant here, and they in succession urged the sand against 

 opposite sides of the stone; -every little particle of sand 

 chipped away its infinitesimal bit of stone, and in the end 

 sculptured these singular forms. 1 



1 "These stones, which have a strong resemblance to works of human art, 

 occur in great abundance, and of various sizes, from half an inch to several 

 inches in length. A large number were exhibited showing the various forms, 



