Under a hot and relatively moist climate, during the Jurassic (-199 to -145 Ma) then the Cretaceous (-145 to -65 Ma) that which would become the Jura resembled a fairly deep, vast marine platform over which the sea regularly advanced and retreated. Thick layers of marl and limestone accumulated formed notably by the numerous fossil remains of the organisms that populated the different marine environments. In the Tertiary period, the sea retreated progressively and the geological strata started to fold as a consequence of the lifting of the Alps.