62 PROCEEDINGS OF THE PRINCETON MEETING 



Mr. Frank Leverett: Caution needs to be exercised in analyzing beach 

 phenomena, for conditions differ in some cases that give an advantage for 

 developing liigli bars that did not obtain at certain other times. Successive 

 beaches also may have the same altitude even if differential uplift or de- 

 pression is in progress, as is shown by numerous observations on the beaches of 

 the glacial lakes. 



Prof. J. W. GoLDTHWAiT : Doctor Davis's evidence will be generally accepted 

 as evidence of suhmergence to a depth less than two feet in historic times. It 

 does not seem to me to be necessarily evidence of suh.ndence of the coast. In 

 view of the great irregularity of the high- tide surface in such harbors as 

 Boston harbor, as Professor Johnson has just shown to occur, and the con- 

 siderable reduction of the area overflowed at high tide by the reclaiming of 

 land along the water front of the city and its suburbs, would not Dr. Davis 

 say that the submergence of less than two feet may be due to a local raising 

 of the high-tide surface rather than to a downward movement of the land? 



Prof. D. W. Johnson : Doctor Davis is right in saying that we ought to find 

 some cases of a lowering of the high-tide surface, producing apparent eleva- 

 tion, if the theory of coastal stability with tidal fluctuations be true : and he 

 will find a number of cases of this very phenomenon cited in my published 

 papers on coastal stability. The person who doubted the existence of any his- 

 torical evidence in favor of subsidence could not have been familiar with the 

 literature, for there is a wealth of published evidence supposed by the authors 

 to prove subsidence within recent historic times — much of this evidence similar 

 to that just presented by Doctor Davis. But it should be noted that the locali- 

 ties mentioned by Doctor Davis are in an area where I have demonstrated a 

 difference of three feet in the elevation of tlie high-tide surface within short 

 distances — an area subject to strong local fluctuations in tide height. All of 

 the phenomena mentioned by him can be easily explained without invoking 

 recent subsidence — the deep peat deposits being of more ancient date than the 

 beach ridges which prove stability, the shallow^ deposits of artificial products 

 having reached their present position through settling of the marsh deposits, 

 local changes in tide levels causing upbuilding of marsh surface, etcetera. 

 The theory of coastal stability satisfactorily accounts for all the facts so far 

 advanced — as Prof. W. M. Davis rightly demands of any theory presented for 

 our consideration — if we recognize the possibility of an early subsidence previ- 

 ous to the period now under discussion, and admit the existence of the local 

 tidal fluctuations which are of such common occurrence along the coast. There 

 fluctuations must have been very marked in the region discussed by Doctor 

 Davis because of dredging, the interfering action of numerous piles for trestles, 

 and natural shoreline changes. 



Further remarks were made by Dr. J. M. Clarke. 



Doctor Davis replied to questions and remarks as follows : 

 To Professor Grabau : The structure and composition of the peat are such 

 that shrinkage and compression to any extent are not possible. The peat 

 below low-tide level is no more compressible than water ; that above is practi- 

 cally silt bound together by roots and stems of grasses. The plant remains in 

 the lower beds show no compression, though fragile. 



