the Displacement of Shore-lines. 495 



is a certain number of alternations. By studying the litera- 

 ture of the Tertiary basins of Europe I have in this way 

 formed a combined profile, which, as regards the alternations 

 of strata, is not yet completed throughout, but which goes 

 from the commencement of the Tertiary to the present time, 

 and which I shall now proceed to describe. 



The mode in which profiles can be compared with the 

 curve to test the correctness of the hypotheses is as follows : — 

 Each arc in the curve will correspond to an oscillation of the 

 sea. It is supposed that under high latitudes the coast-lines 

 move up and down with the curve. Such an oscillation I call 

 a " geological stage." Each arc will therefore have its corre- 

 sponding oscillation or " stage," and in each " stage " there 

 will be as many alternations of strata as there are precessional 

 periods in the corresponding arc. When the eccentricity 

 only sinks inconsiderably between two or more arcs, the arcs 

 run into one another and form, as it were, ranges with two or 

 three small summits. We have then " stages " wath more 

 oscillations and more alternations of strata than the ordinary 

 ones. We shall see examples of this in what follows. We 

 can draw a line which indicates the boundary between marine 

 and freshwater formations. This line may be nearly or quite 

 horizontal. Whether it is to be drawn high or low depends 

 upon how much above the sea the place was situated where 

 the deposits were formed at the time when the deposition 

 took place. The higher it lay, the higher must the line 

 be drawn. The place may have been so elevated that it 

 never was submerged. Then the lines are situated higher 

 than the curve, and all the deposits are freshwater or terres- 

 trial formations. But it may have lain so low that it never 

 rose above the sea, and all the deposits are marine formations. 

 But the line may cut the curve. Then marine formations 

 alternate with land- and freshwater-formations. The former 

 correspond to those arcs of the curve which project above the 

 line; the latter to those which lie below it. And when there 

 are no gaps in the series of deposits, there will be as many 

 alternations of deposits in the marine, freshw^ater, and terres- 

 trial formations as there are precessional periods in the cor- 

 responding arcs of the curve. 



As a starting-point 1 will take the profile of the Paris- 

 basin*, which I will endeavour to join on to recent times. 

 Afterwards I will refer to the lower and middle parts of the 

 Eocene period. 



The section of the Paris-basin about Mery-sur-Oise {Bull. 



* This section is given in my memoir on Alternations of Strata. 

 2 L 2 



