in Massachusetts. 79 



harbor the salt marsh has so much increased, that three 

 hundred tons of hay are now cut annually, where only 

 flats existed forty years ago. 



Monomoy Beach extends southerly from Chatham to- 

 wards Nantucket, and was formed by increments at its 

 southern extremity. A few years since the sea made a 

 breach across its northern part, so that it is now an 

 island. 



Sandy Neck extends eastward nearly across Barnsta- 

 ble harbor, and continues to advance in an easterly 

 direction. 



Smith's Point, which forms the southeastern extremity 

 of Nantucket, was nearly in the same situation when Des 

 Barres constructed his chart, as at present. But since 

 that time it has been shortened a mile or two, and again 

 extended. 



Details of this kind might be multiplied were it neces- 

 sary ; but they are not of much use to geology, unless 

 the precise rate of advancement and retrogression can be 

 ascertained. 



Such facts make one feel as if such low sandy islands 

 as Nantucket were slidino: beneath his feet. But that no 



large island on our coast has been very essentially chang- 

 ed since man was placed on the globe, is evident from 

 the fact, that their shores often exhibit cliffs of clay and 

 sand in regular layers, constituting a distinct tertiary 

 formation, whose period of deposition must be placed 

 earlier than the creation of man. 



DUNES, OR DOWNS. 



Frequently on the coast, the sand is carried up so far 

 upon the land by the waves and spray, that the reflux 



"H 



