GEOLOGICAL AGE AND FORMATION. 41 



been altered since. When first built, it was only an ex- 

 tremely high storm-tide that would stop it ; now, a com- 

 mon perigee tide will stop it ; and it is stopped in this way 

 perhaps twenty times in a year. Judge Goffe, my informant, 

 is of opinion, that the tide rises on the wheel fifteen inches 

 higher than at first, and he is sure it is not less than twelve 

 inches. 



The saw-mill on Sluice Creek, owned by Mr. Clinton Lud- 

 1am, has been built a hundred years. It is a pond mill, 

 and from the old papers in Mr. Ludlam's possession, he is 

 well satisfied that it was originally located so as to be out 

 of the reach of ordinary high tides. Now, such a tide 

 would come half way up the mill-dam j and the mill is 

 only kept in operation by a dam and sluice some distance 

 below. Judging from all the facts, he thinks the tides rise, 

 on an average, at least two feet higher than when the mill 

 was built. 



These measurements agree in giving the rate of sub- 

 sidence as about two feet in a century, or one quarter of 

 an inch a year ; a conclusion which was arrived at in my 

 Annual Keport of last year from observations in other 

 counties of the State.* 



The whole amount of this subsidence is not known ; it 



* The facts as to the rate of subsidence given last year, were, that below Hancooli's 

 Bridge, over AUoway's Creek, in Salem County, the sluices in a meadow bank, built about 

 the year 1700, are full three feet below low-water mark; so low that my informant had 

 only seen them twice in thirty years. On the opposite bank of the creek is an oak stump 

 standing, the roots of which are in hard bottom, and the top of it, where cut uS, is about the 

 level of high tide. It has been cut by an axe; and, of course, has been cut since the set- 

 tlement of the country, or within about one hundred and fifty years. The tides would have 

 killed a tree in that location when they were three feet lower than now. A settling of 

 three feet in a hundred and fifty years, or a rate of subsidence of about two feet in a cen- 

 tury, is shown by these facts. 



