346 Tattle — Changes in Elevation of Land and Sea. 



atmospheric pressure, and the resulting changes in wind 

 velocities. 



(2d) The above oscillations compensate themselves com- 

 pletely in the course of time, and do not give rise to a continu- 

 ous movement in a given direction. 



(3d) That in addition to the above movements of the sea some 

 ports show a more or less continuous rising of the sea rela- 

 tively to the adjacent land ; others a lowering of the sea level 

 in its relation to the land, and still others maintain a constant 

 relation between the two. These latter . make it clear that 

 except for the periodic changes noted above, the sea does not 

 change its level, and that the relative changes are due to land 

 movements. 



(4th) At various ports the rate of change in the elevation of 

 mean sea level referred to the adjacent land has not remained 

 constant, but has varied in a considerable degree. All the 

 observations show that for long periods the rate of change is 

 less than took place in some part of that period, and the evi- 

 dence is strong that the movement is not continuous, but oscil- 

 latory and confined within narrow limits. 



(5th) The observations at New York City show that since 

 1875 the land has been subsiding relatively to mean sea level 

 by about 145 ft. per century, but from the establishment of 

 the self -registering tide gauge in 1853 to that date, little or no 

 change had occurred, and it is improbable that the present rate 

 of subsidence will be continued indefinitely. 



