1889 ] THE DISPLACEMENT OF BEACH-LINES. 55 



connected the profile of the Basin of Paris with the present 

 time. We will now trace the oscillations backwards, as far as 

 the close of the Cretaceous period, in order to see, if possible, 

 how many oscillations the geological period which is called the 

 Tertiary contained. 



The Cretaceous period is divided from the Tertiary by 

 a period of denudation, in which the land lay high in rela- 

 tion to the sea. The oldest marine formation in Europe, from 

 the Tertiary period, is considered to be that at Mons in Belgium. 

 It indicates the first oscillation, but that deluge does not 

 appear to have left any traces iu the other Tertiary basins. 

 The first Tertiary deluge of the sea in the Paris basin formed 

 the conglomerate at Rilly and Nemours. It was followed by 

 an upheaval of the land, and the marine conglomerate became 

 covered by the Rilly fresh-water lime-stone. To this oscil- 

 lation in the Paris basin corresponds, probably, in Belgium, 

 the so-called „systeme Heersien", at the bottom a purely ma- 

 rine formation, at the top containing, remains of land-plants. 

 Then a new oscillation occurred and now England became 

 partly covered by the sea. Here was deposited the marine 

 Thanet sand, and over it the Woolwich and Reading series (Plas- 

 tic clay), which is partly a brackish and fresh-water stage, and 

 which shows that the beach-line had again retreated. In Bel- 

 gium was formed, during that oscillation, the cysteine Lande- 

 aien", at the bottom a purely marine formation and at the top 

 brackish. In the Paris basin the marine sand at Bracheux was 

 formed, and was followed by a fresh-water formation containing 

 h'own-coal (Lignites de Soissonais). Now followed a new rising 

 of the sea level and after that again an upheaval. This has 

 ieft no trace in the Basin of Paris, but, in England, the London 

 °lay was formed, and in Belgium the „systeme Ypresien." Lon- 

 don clay begins with a littoral formation of shingle or gravel 

 (Oldhavenbeds), and the upper part of the stage shows that the 

 again became shallower in consequence of a new upheaval 

 °f the land. This stage, as was shown above, contains at least 11 al- 

 ternations, and therefore probably corresponds with at least two arcs 



