30 . On the Revolutions which have 



number of species of marine animals perished, and were replaced 

 by beings which did not previously exist : among the latter even 

 fishes are met with. 



We cannot determine the duration of this period of repose, 

 but every thing leads to the conclusion that it was troubled by a 

 new catastrophe the soulevement of our calcareous Alps. This 

 powerful convulsion was not limited solely to these last ; it reach- 

 ed the Jura, laying it almost completely dry ; or in other words, 

 elevating it to a still greater height, so that the sea retired from 

 the valleys which it had hitherto overflowed, and exposed the 

 chalk it had deposited in them.* 



At this epoch the chalk formed the bottom of the sea, and as 

 its thickness was not nearly so great as the height of the Alps 

 above their base, this rock forms only the summits of these 

 mountains, whilst the rest belong to the Jurassic limestone, 

 which in its lower beds belongs to the Lias, and in its upper to 

 the Oolitic formation. But, owing to dislocations, ruptures and 

 boulever semens, the chalk is in many places destroyed, whilst 

 at the same time it makes its appearance at very different heights ; 

 and in positions where it could not be found if those soulevemens 

 had happened slowly and without violence. 



However, neither the Alps nor the Jura had attained by this 

 new catastrophe the height which they were afterwards to reach. 

 The sea did not retire completely from the country ; it still ex- 

 tended an arm between the two chains. 



It is in this canal or strait that we find a new formation of 

 rocks, and a new creation of genera and species of animals. The 

 rock which the sea deposited at that time is of a sedimentary 

 structure, that is to say, it is extended in beds, and is composed 

 of fragments of pre-existing rocks united together by a cement 

 which is sometimes argillaceous, sometimes calcareous. When 

 the fragments are very small we know it by the name of Mo- 

 lasse ; the fragments are generally polyhedral, and the cement 

 argillaceous. 



* Chalk which in many localities, but not within the Canton, is white and 

 friable, is with us generally of a deep grey colour, and of sufficient hardness 

 to receive a pretty fine polish. It can only be recognised by the nature of 

 the organic bodies which it contains, and which are the same as those of the 

 white and friable chalk. 



