334 Tuttle — Changes in Elevation of Land and Sea. 



land, which has been quoted by many authorities, rests on the 

 above evidence, and is manifestly open to doubt and uncer- 

 tainty, as he recognized when he wrote in his 1885 report, that 

 "we find conclusive evidence of a general subsidence of the 

 coast, or rise of water level to an extent of from ten to twenty 

 feet within a short period of geologic time, but at a rate which 

 is not quite definitely established." Professor Cook further- 

 more stated in his report of the Geology of New Jersey in 

 1868, that "this movement is one of a series which has occurred 

 on our coast by which the line of water level has been alter- 

 nately elevated and depressed, the whole range being confined 

 within twenty feet." 



Others have since frequently expressed the same ideas, but 

 as they probably made use to a large extent of Professor Cook's 

 opinions and evidence, it will be needless to quote them. 



The self -registering tide gauge had only recently been made 

 use of when Professor Cook read his paper, and tidal observa- 

 tions could not be obtained to determine the rate of subsidence, 

 but since that date long series of tidal observations have become 

 available, and it is proposed to develop in this paper what such 

 observations in New York Harbor can tell as to the relative 

 changes in the elevation of earth and sea in the vicinity. 



The tidal observations at JSTew York, which are of impor- 

 tance, start from the year 1853, when a self-registering tide 

 gauge v^as put in operation by the Coast Survey at Governor's 

 Island, and maintained up to and including the year 1879, when 

 the series terminated. We also have the records of a self-regis- 

 tering gauge maintained by the Coast and Geodetic Survey dur- 

 ing the years 1876-92, at Sandy Hook, 'N. J., records of self- 

 registering gauges of the Department of Docks and Ferries from 

 1888-1903, at Pier A, West 57th St., and from 1894-1903 at 

 East 24th st., in New York City, besides the record from a 

 self -registering tide gauge of the Coast and Geodetic Survev at 

 Fort Hamilton, for the years 1893-1902.* 



The observations at Governor's Island were all referred to 

 B. M.,f which was established about the year 1853 by the 

 Coast Survey and. is still in existence. Levels were run from 

 this bench mark to other benches, in 1875 and again in 1886. 

 The differences found at those times were checked in 1898 

 and 1900 and found correct, so that we may be confident that 

 since 1875 B. M M has not settled or been otherwise disturbed. 



The datum plane used in this paper is mean low water — 



* The writer is indebted to the U. S. Coast and Geodetic Survey and to the 

 Department of Docks and Ferries, New York City, for tidal data not hitherto 

 published. 



f For description see C. and G. S. Keport 1887, app. 14, p. 293. 



" 1899, app. 8, p. 555. 



