CHANGES OF LEVEL. 249 



middle of the Cretaceous period. At the period of the Upper 

 Cretaceous formation the land again began to rise ; the sea dis- 

 appeared from the region of the Jura, which, during the whole 

 Eocene period was converted into dry land (see vol. i. p. 271 et 

 seqq.) ; and this upheaval was continued until the end of the 

 Aquitanian stage of the Miocene period, the sea disappearing 

 also from the region of the Alps, and leaving only a few lagoons, 

 which then became converted into freshwater lakes, so that when 

 the upheaval had attained its maximum the sea for the first time 

 retired from Switzerland. During this long period of elevation 

 a partial upheaval must also have taken place in the direction 

 of the Alps after the deposition of the Nummulitic Limestone 

 and the Flysch, by which the whole region of the Alps was 

 finally removed from the influence of the sea. On the other 

 hand, during the Tongrian period, a depression must have 

 occurred in the north-west of Switzerland, permitting the 

 Tongrian sea to penetrate as far as Basle, Porrentruy, and 

 Delsberg. 



A continental depression commenced, however, at the time of 

 the formation of the Grey Miocene, and attained its maximum 

 during the Helvetian stage, by which the Swiss low grounds 

 were once more covered by the sea. This was followed again by 

 a continental upheaval, so that at the time of the Upper Brown- 

 coal formation (in the CEningian stage) all the land was above 

 the level of the sea, and even the masses of sand and stone which 

 had been washed into the sea were elevated. The last upheaval 

 took place at a later period, after the whole of the stages of the 

 Swiss Miocene had been deposited ; and this upheaval is the most 

 important of all, as it caused the present configuration of Swit- 

 zerland. The Miocene is deposited horizontally in the Swiss 

 low grounds, and is upraised in the vicinity of the Alps, and 

 along the whole Alpine chain is not only thrown up in the shape 

 of a roof * (vol. i. p. 287), but is for a great extent even covered 



* On the geological map the direction of this anticlinal line is indicated, 

 which may be traced from the valley of the Rhine to Geneva. In Eastern 

 Switzerland two folds may be recognized in it ; so that two arches have been 

 formed, which, however, have been pressed close to one another. 



