the Displacement of Shore-lines. 505 



deposits, the Perforata-heds : — from below upwards — (a) an 

 oyster-bed, (/3) argillaceous marl, (y) calcareous marl ("lower 

 striata-horizon "), (8) a shell-bed (" lower perforata-horizon''), 

 (ej clay (" upper striata horizon," second oscillation ?), 

 iX) clay with a few hard marly beds and the same fossils as 

 in ^, (rj) another oyster-bed, (^) clay with oysters, (t) cal- 

 careous marl (" upper perforata horizon," third oscillation ?) ; 

 above this the Ostrea-clay^ a thick clay with oysters and 

 marly beds, and with a sandy calcareous bed in the middle 

 (fourth oscillation). Over this again the Tjower Coarse 

 limestone, generally in two thick beds (fifth oscillation), 

 covered by a thick bed of clay varied with layers of sand, 

 probably a freshwater formation, and covered by freshwater 

 limestone. Finally, the last (6th) oscillation, the Upper 

 Gypsum horizon, gypsum alternating with clay ; and above it 

 coarse limestone alternating with gypsum ; in other places 

 clay with Foraminifera, marine: — the Upper Coarse limestone, 

 I have cited all these details in order to show that these beds, 

 which are all contemporaneous with the " Calcaire grossier " 

 of Paris, seem to indicate six oscillations. 



Above the "Calcaire grossier''' the Upper Eocene com- 

 mences with the continuous series of the Paris basin, which 

 has already been described. 



The Lower and Middle Eocene therefore appear to include 

 12 oscillations, six of which pertain to each of the two 

 divisions of the formation. By this the first cycle of the 

 curve is filled up ; so that the beginning of the cycle will 

 about fall upon the boundary between Cretaceous and Eocene. 

 In the Paris-basin the Middle Eocene has 25 alternations of 

 strata, and perhaps one or two breaks. Six oscillations about 

 correspond to 25-30 precessional periods. 



At the commencement of the cycles the mean value of the 

 eccentricity is low ; it rises in the middle of the cycle, and 

 sinks again towards the conclusion. The position of the 

 shore-lines must also depend upon the mean value of the 

 eccentricity. But as it increases very slowly through very 

 long periods, it will be very long before its action is to be 

 seen on the solid earth. The middle of the cycles ought thus 

 to correspond to the overflows of the sea, the beginning 

 and close to the periods of denudation which separate the 

 formations. Breaks in the series of beds may therefore be 

 expected under high latitudes, especially at the limits between 

 the cycles. 



The boundary between Cretaceous and Eocene is indicated 

 by what Suess (Antlitz der Erde,'\\. 7ter Abschn. p. 376) calls 

 a negative phase : the sea had retreated in higher latitudes. 



