s 



80 



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Causes of Geological Change 



waves do not force it back. After it is dried, the sea 

 breezes force it still further inland ; and in the course of 

 time, ridges of considerable elevation are formed. These 

 constitute those moving sand hills, which, on the eastern 

 continent, especially on the banks of the Nile, are so 

 famous under the name of dunes or downs. On the 

 shores of Cape Cod they are very common, and are 

 soqaetimes as much as sixty or seventy feet high. At 

 the eastern extremity of the Cape they move westward ; 

 and they threaten at present the village and harbor of 

 Provincetown, if not arrested by the beach grass, which 

 has recently been transplanted to their summits by order 

 of government. I cannot learn that any of the dunes of 

 Cape Cod have yet produced much injury to farms or 

 villages, as they have done on the eastern continent. 

 The sands of Africa, it is well known, have advanced as 

 far as the Nile, burying cities and fertile regions of great 

 extent. And it would be strange if the future history of 

 the southeast part of Massachusetts should not contain 

 catastrophes of a similar kind, though of far more limited 

 extent. 



But few dunes occur in the interior of Massachusetts. 

 In the valley of the Connecticut I have noticed them on 



Monta 



Ct. 



.1- 



These, in consequence of the prevalence of northwest 

 and westerly winds, are slowly advancing towards the 

 southeast. 



ICE FLOODS. 



Whoe 



m a mountamous region, after a severe winter, when its 



b 



