Tuttle — Changes in Elevation of Land and Sea. 345 



explain these secular changes in mean sea level, and if such 

 changes did occur, they could hardly explain the difference in 

 amount and direction of the changes of sea level observed at 

 different points. Besides, it is seen from tidal observations on 

 the German coast of the Baltic Sea, the North Sea, and the 

 coast of India, that no continuous change in ocean level has 

 occurred in those places, which would probably be the case 

 if there had been any great or long continued change in abso- 

 lute ocean levels elsewhere. 



We must conclude then, except for minor variations due to 

 meteorological conditions, that it is the land and not the sea 

 which is changing in elevation. 



Most of the geological evidence appears to show that the 

 movement of the land relatively to the sea in recent geologic 

 .times has been of a C} T clic character and confined within narrow 

 limits. There is little geologic evidence to be found in the 

 vicinity o{ ISTew York of a definite character to indicate depres- 

 sion. It is true that marsh sod can be found outshore from 

 the beach, and below mean sea level ; that cedar trees die out 

 on the shore, and that peat bogs and stumps of trees have been 

 found in many places below sea level. These phenomena are 

 to be explained, however, by the inroads of the sea during 

 storms, and by wave action ; as well as by the compression and 

 consolidation of the marsh land, which has been known to sink 

 as much as three feet when drained, or loaded with sand. As 

 we leave the shore these apparent evidences of subsidence dis- 

 appear and in places thoroughly protected from the sea few or 

 none of them are found. 



It does not appear from the evidence presented by tidal 

 records, or from historic or geologic evidence, that our sea-coast 

 is in any immediate or serious danger from subsidence of the 

 land, for almost without exception the longest records show 

 the least change, and were it not for the power and efficiency 

 of modern dredging machinery the shoaling of harbors would 

 probably be a more serious affair. 



The tidal observations have been taken for so short a time, 

 however, that they can only tell us what has been going on 

 recently, and do not disprove a possible change in ocean eleva- 

 tion too small to be detected within the period of observation. 



In conclusion it may be stated with confidence, as the result 

 of an inspection and study of tidal observations on both sides 

 of the Atlantic for the first time brought together, 



(1st) That the mean sea level oscillates in an irregular 

 manner, having an average period of about eight years. These 

 oscillations closely resemble one another at many ports distant 

 from each other, and appear to be largely due to changes in 



