Shaler.] 128 [October 7, 



Mr. Shaler presented the following paper : — 



On the Nature of the Movements Involved in the 

 Changes of Level of Shore Lines. By JV. S. Shaler. 



Accurate observations on the changes of position of the earth's sur- 

 face at different points have been thus far limited to the lines where 

 the sea and land meet. 



Nowhere away from shores are there means by which alterations of 

 elevations can be detected by easily made comparisons. The habits 

 of men cause the shghtest changes of the sea level to be immediately 

 noticed, so that all modifications of the shore line meet with atten- 

 tion, while alterations of far greater extent, at points remote from the 

 sea, would pass unregarded. Nor can we expect, in the present im- 

 perfect method of determining the contour of inland irregularities of 

 surface, much more accm*ate data from which to decide whether any 

 region maintains over its whole surface the same relative level duripg 

 considerable periods of time. Even the most trustworthy methods of 

 determining relative levels of points remote from shores are so liable 

 to accidental errors, that it is doubtful whether unquestionable obser- 

 vations are to be attained. Being thus limited to the shore line for 

 our accurate data concerning elevations and depressions of the land, 

 it becomes a matter of first importance to determine what are the 

 valid deductions which can be made from the observations we 

 may obtain there. We should ascertain how far the upward and 

 downward movements indicated by the unerring water level can be 

 attributed to the general area in which the shore lies, before the true 

 value of these movements as indices of geological changes can be 

 determined. At first sight it would seem an unnecessary labor to ex- 

 amine a question which appears so perfectly clear in all its bearings ; 

 it certainly looks unlikely that elevation or subsidence of the shore 

 could indicate anything but the general rising or sinking of the land 

 area to which it belongs, yet, on examination, it will be easily seen 

 that these indications are far from being as decisive as would at first 

 be supposed. 



Before entering upon the question of the cause of those movements 

 of the solid surface of the earth, which result in the changes of level 

 at the shore line, it is necessary to attend to some of the more gen- 

 eral facts deducible from the phenomena. The most important result 

 of the observations which have been made, is that the movements 

 are in no case local, that is, no portion of shore of a mile, or even a 



