128 Scientific Geology. 



harbor, has been covered up, and now begins to be disinterred on the 

 eastern shore. A similar change of sides has taken place in a peat 

 swamp on Nauset Beach ; which lies north of Chatham Beach, join- 

 ing the main land at Eastham. 



I have described, in the second part of this Report, two excavations 

 in solid rock in Newport, Rhode Island ; one of which is called Pur- 

 gatory ; and these may be taken as a good example of the action of 

 the sea upon a rocky shore. 



Gain of the Land upon the Sea. 



Very frequently the materials that have been swept away by the 

 sea, are again deposited by tides and currents along the same coast, 

 forming low beaches. This is the case in nearly all the instances on 

 our coast where the land is wasting away. Perhaps the most re- 

 markable example is Chatham Beach, at the southeastern extremity of 

 Cape Cod, which was probably all formed in this manner. On the 

 Cape I was informed that this beach had advanced southerly, during 

 the last 40 years, at the rate of a mile in 8 years. Des Barres con- 

 structed a chart of this coast in 1772, and he says that the gain of 

 this beach, for 30 years previous to that period, was 21-2 miles, that 

 is a mile every 12 years. 



An intelligent writer in the Barnstable Journal, however, has re- 

 cently stated, that it has advanced southerly only three miles in 70 

 years. He says that 20 years ago, this beach was an island ; and 

 that there was a good harbor near its northern termination, which is 

 now entirely filled up ; so that no indentation of the coast marks its 

 former situation. Webb's island, also, formerly situated not far from 

 this harbor, is entirely washed away. In consequence of these 

 changes, it is well known that the harbor of Chatham, once excel- 

 lent, is nearly ruined ; and nothing can save it from complete destruc- 

 tion but the forming of a new entrance. 



Nauset Beach, already referred to, has likewise extended, accord- 

 ing to the same writer, a mile southerly in 50 years ; and it can ex- 

 tend no farther in that direction. In Nauset harbor the salt marsh 

 has so much increased within 40 years, that 300 tons of salt grass 

 are now cut where at that time only flats existed. 



Monomoy Beach extends southerly from Chatham towards Nan- 

 tucket ; and has been formed in a similar manner by increments at 

 its southern extremity. Not long ago the sea broke across the north- 

 ern part of this beach, so that it is now an island. 



