742 ABSTRACTS OF PAPERS 



by him temliiijr to show that there had not been any marked change in the 

 relative level of land and sea aloni; the southwest coast of Hudson's Bay 

 within the last two or three hundred years ; certainly nothing like 5 feet in 

 that length of time. His evidence is based on a comparison of carefully 

 made maps. If his interpretation is correct, it is an interesting example of 

 coastal stability farther north than our observations have extended. 



Replying to Dr. Davis, it is true that the physiographic evidence of coastal 

 stability is not as sensitive as one cimld wish. All physiograi)hers will recog- 

 nize the difficulty of proving absolute stability by beach ridges which may 

 vary in height several feet. On tlie other hand, the physiographic evidence 

 is very reliable and seems to prove conclusively that there can have been no 

 marked subsidence of the coast for several thousand years : certainly the 

 deei)ly buried peat can not possibly be explained on the theorj' of recent sub- 

 sidence, for the beach ridges prove that the coast can not have subsided more 

 than a very few feet at most, whereas the peat descends to much greater 

 depths. 



I believe I have never held that there can have been no subsidence what- 

 ever in recent times. I have always held that tlie physiographic evidence did 

 not preclude the possibility of a slight subsidence in the last few thousand 

 years. On the other hand, I have held, and still believe, that there is no 

 reliable evidence that even a slight subsidence has occurred in recent times. 

 Tidal fluctuations and other shore changes will account for the apparent evi- 

 dences of subsidence. 



Dr. Davis seems to believe that only gradual changes in the relative levels 

 of land and sea could account for the dead stumps he has described, and that 

 therefore the theory of tidal fluctuations will not account for them. I should 

 have said that inasmuch as changes in the form of the shore often take place 

 gradually, the local rises of the high tide surface which produce apparent 

 subsidence also take place gradually. Only in exceptional cases is the rise 

 so sudden as in the Scituate case which I" described. 



SOME COASTAL MARSHES SOUTH OF CAPE COD 

 BY CHARI>ES A. DAVIS 



(Al)stTact) 



A report on a continuation of the work on salt marshes in the vicinity of 

 Boston, the results of which were reported at the Boston meeting in 1909. 

 The structure of salt and brackish marshes on the south side of Cape Cod 

 and on Long Island is described, and the evidence this bears in favor of recent 

 coastal subsidence is discussed. 



Discussion 



Prof. J. B. WooDWORTH remarked on the apparent validity of the argument 

 for subsidence based upon the structure of Spartina patens marshes and the 

 contradictory evidence as to a very recent subsidence of the coast ix)inted out 

 by Prof. D. W. Johnson from his finding successive beach crests of ancient 



