1889.] THE DISPLACEMENT OF BEACH-LINES. 43 



Many difficulties are still met with in that work. First and 

 foremost the calculation of the curve is in itself not absolutely 

 to be depended on for the more ancient times. This difficulty 

 is, however, to a certain extent, surmounted by the fact that the 

 curve repeats itself, so that it is probably not of great im- 

 portance. 



Another difficulty is to find long and accurately described 

 profiles free of gaps in the series of beds. Profile-surveys are 

 not sufficient. Geologists frequently only indicate, that there 

 are some, it may be a few or many alternations of strata, with- 

 out definitely stating the number. 



A third difficulty lies in the separation of the alternation 

 which is owing to precession, and that based on other more tem- 

 porary and local relations. Especially is this difficulty per- 

 ceptible in shore formations, but it has proved to be less than 

 I had at first supposed. 



A fourth difficulty lies in deciding the number of oscillations 

 of the beach-lines. The higher the spot was situated, the more 

 rarely was it flooded; the deeper it lay the more rarely was it 

 raised above the sea. And the movement of the solid crust ol 

 the Earth has, as might be supposed, not been everywhere so 

 uniform as that of the sea. 



A fifth dificulty lies in the finding of perfectly typical pro- 

 files of the stages produced by the oscillations. As the sea 

 rose and fell slowly, the number of the marine alternations of 

 strata would be less and that of land and fresh-water formations 

 greater, the higher the place lay, and the shorter the time was in 

 which it lay sunk in the sea during each oscillation. But this 

 difficulty is only of importance when the continuous profiles are 

 so short that thev do not nass through several oscillations. 



